The graph of this approximation function C (x, y) is a flat plane passing through the graph of our function at the point (x 0, y 0, f (x 0, y 0)) . Below is a video showing how this approximation changes as we move the point ( x 0 , y 0 ) around.Question: Use the tangent plane approximation to calculate approximately how much more area a rectangle that is 5.01 by 3.02 cm has than one which is 5 by 3 . Draw a diagram showing the smaller rectangle inside the enlarged rectangle. On this diagram clearly indicate rectangles corresponding to the two torms in the tangent line approximation.Tangent Plane. Determine the plane touching a surface at a given point. Tangential Component of Acceleration. Measure acceleration in the direction of motion. Taylor …Note that since two lines in \(\mathbb{R}^ 3\) determine a plane, then the two tangent lines to the surface \(z = f (x, y)\) in the \(x\) and \(y\) directions described in Figure 2.3.1 are contained in the tangent plane at that point, if the tangent plane exists at that point. The existence of those two tangent lines does not by itself ...This means that the equation of the tangent plane is $ z – 2 = -4(x + 2) – 2(y – 1)$ or $ z = -4x – 2y -4$. Linear Approximation: Application of Tangent Planes. Through tangent planes, we can now approximate the linearization of functions. Notice how the resulting tangent plane returns a linear equation?Working in "clothoid space" you can calculate the angle P1P2 P 1 P 2 with the x′ x ′ axis. Adding the t1 t 1 angle you get the angle for the line P1toC1 P 1 t o C 1. With the distances and this angle you solve the triangle can calculate rp r p. Now build a circumference of center = C1 C 1 and radius rp r p.Free slope calculator - find the ... System of Inequalities Polynomials Rationales Complex Numbers Polar/Cartesian Functions Arithmetic & Comp. Coordinate Geometry Plane Geometry Solid Geometry Conic Sections Trigonometry. Calculus. Derivatives Derivative Applications Limits Integrals Integral Applications Integral Approximation Series ODE ...Tangent Plane to the Surface Calculator At the point (x, y) At the point (x, z) At the point (y, z) − Various methods (if possible) − Use a formula Use the gradient Figure 12.21: A surface and directional tangent lines in Example 12.7.1. To find the equation of the tangent line in the direction of →v , we first find the unit vector in the direction of →v : →u = − 1 / √2, 1 / √2 . The directional derivative at (π / 2, π, 2) in the direction of →u is.Equations Of Tangent Planes. If we zoom in small enough to a point on a surface, we can approximate the function by a linear function of two variables. First, let’s …Explore math with our beautiful, free online graphing calculator. Graph functions, plot points, visualize algebraic equations, add sliders, animate graphs, and more.Derivatives Derivative Applications Limits Integrals Integral Applications Integral Approximation Series ODE Multivariable Calculus Laplace Transform Taylor/Maclaurin Series Fourier Series Fourier Transform. ... tangent line approximation. en. Related Symbolab blog posts. Practice, practice, practice. ... BMI Calculator Calorie Calculator …Free tangent line calculator - find the equation of the tangent line given a point or the intercept step-by-stepAt time stamp. 2:50. , Sal is calculating the value of the linear approximation using the point slope formula in the form, (y-y1)/ (x-x1)=b, and he points to b and calls it the slope. But I always thought that b was the y intercept. So b would be equal to: (y-y1) – m (x-x1)=b, and that would be the y intercept, not the slope.Why not just use the equation and a calculator? In the real world, there is often not an equation, but just data that describe a situation, and an approximation ...This means that our linear approximation, L of xy, is equal to 1 minus 2 open parenthesis x minus 4 close parentheses plus 3 open parentheses y minus 1 close parentheses. And we can evaluate this to find L of 4.1 comma 0.9 is approximately 0.5. So on our tangent plane, f of 4.1 comma 0.9, is about 0.5. Mar 22, 2023 · Determine the equation of a plane tangent to a given surface at a point. Use the tangent plane to approximate a function of two variables at a point. Explain when a function of two variables is differentiable. Use the total differential to approximate the change in a function of two variables. This is also known as tangent line approximation, which is the method of determining the line equation that is nearer estimation for entered linear functions at any given value of x. So, the linear approximation calculator approximates the value of the function and finds the derivative of the function to evaluate the derivative to find slope ... Free tangent line calculator - find the equation of the tangent line given a point or the intercept step-by-stepJul 12, 2022 · By knowing both a point on the line and the slope of the line we are thus able to find the equation of the tangent line. Preview Activity 1.8.1 will refresh these concepts through a key example and set the stage for further study. Preview Activity 1.8.1. Consider the function y = g(x) = − x2 + 3x + 2. Desmos offers best-in-class calculators, digital math activities, and curriculum to help every student love math and love learning math.Calculator to give out the tangent value of a degree. Tangent Calculator. The tangent of an angle is the ratio of the length of the opposite side to the length of the adjacent side: so called because it can be represented as a line segment tangent to the circle, that is the line that touches the circle, from Latin linea tangens or touching line (cf. tangere, to touch).Compute answers using Wolfram's breakthrough technology & knowledgebase, relied on by millions of students & professionals. For math, science, nutrition, history ...Free quadratic equation calculator - Solve quadratic equations using factoring, complete the square and the quadratic formula step-by-stepFurthermore the plane that is used to find the linear approximation is also the tangent plane to the surface at the point (x0, y0). Figure 14.4.5: Using a tangent plane for linear approximation at a point. Given the function f(x, y) = √41 − 4x2 − y2, approximate f(2.1, 2.9) using point (2, 3) for (x0, y0).In order to give an equation for the tangent plane on the previous slides, we need to nd suitable vectors to serve as # n and r# 0. Finding r# 0 Let’s begin with r# 0. Notice that the tangent lines T 1 and T 2 pass through the point P on the graph of f(x;y). Therefore the tangent plane, which contains both tangent lines, does, too.Then the plane that contains both tangent lines T 1 and T 2 is called the tangent plane to the surface S at the point P. Equation of Tangent Plane: An equation of the tangent plane to the surface z = f(x;y) at the point P(x 0;y 0;z 0) is z z 0 = f x(x 0;y 0)(x x 0) + f y(x 0;y 0)(y y 0) Note how this is similar to the equation of a tangent line.Figure 3.5.4: Linear approximation of a function in one variable. The tangent line can be used as an approximation to the function f(x) for values of x reasonably close to x = a. When working with a function of two variables, the tangent line is replaced by a tangent plane, but the approximation idea is much the same.Because the binormal vector is defined to be the cross product of the unit tangent and unit normal vector we then know that the binormal vector is orthogonal to both the tangent vector and the normal vector. Example 3 Find the normal and binormal vectors for →r (t) = t,3sint,3cost r → ( t) = t, 3 sin t, 3 cos t . Show Solution. In this ...A) Find the plane tangent to the graph of the function in P = (2, 0) and calculate the linear approximation of the function in (1.9, 0.1). B) Find the dire Find the equation for a plane which is tangent to the graph of the function f(x,y) = x^3 + 3x^2y - y^2 - …A right triangle with two sides formed from the radii of a circle and the third side tangent to the circle. As long as the angle \theta θ is sufficiently small, the length of s s ( ( the arc subtended by \theta) θ) is very close to that of s^ {\prime} s′, the third side of the triangle. The small-angle approximation thus corresponds to s ...The graph of this plane curve appears in the following graph. Figure \(\PageIndex{5}\): Graph of the plane curve described by the parametric equations in part c. This is the graph of a circle with radius 4 centered at the origin, with a counterclockwise orientation. The starting point and ending points of the curve both have coordinates \((4,0)\).Drag P P along the parabola or enter the x-coordinate for point P P . Notice how the equation of the tangent line changes as you move point P P . What happens when x = 0 x = 0 for this function? What about as |x| | x | gets large? Now that we can find the tangent to a curve at a point, of what use is this?Mar 22, 2023 · Determine the equation of a plane tangent to a given surface at a point. Use the tangent plane to approximate a function of two variables at a point. Explain when a function of two variables is differentiable. Use the total differential to approximate the change in a function of two variables. Slope of Tangent Line—Instantaneous Rate of Change. The slope of the tangent line to the graph of a function y = f(x) at the point P = (x, f(x)) is given by. m = lim Δx → 0f(x + Δx) − f(x) Δx, provided this limit exists. Note: The slope of the tangent line is also referred to as the insantaneous rate of change of f at x.What we need to do now is determine the equation of the tangent plane. We know that the general equation of a plane is given by, a(x−x0)+b(y −y0)+c(z −z0) = 0 a ( x − x 0) + b ( y − y 0) + c ( z − z 0) = 0 where (x0,y0,z0) ( x 0, y 0, z 0) is a point that is on the plane, which we have. Let’s rewrite this a little.Question: Use the tangent plane approximation to calculate approximately how much more area a rectangle that is 5.01 by 3.02 cm has than one which is 5 by 3. Draw a diagram showing the smaller rectangle inside the enlarged rectangle. On this diagram clearly indicate rectangles corresponding to the two terms in the tangent line approximation.Graphing Calculator. A free online 2D graphing calculator (plotter), or curve calculator, that can plot piecewise, linear, quadratic, cubic, quartic, polynomial, trigonometric, hyperbolic, exponential, logarithmic, inverse functions given in different forms: explicit, implicit, polar, and parametric. It can also graph conic sections, arbitrary ...Answer. Figure 2.7.5 shows a portion of the graph of the function f(x, y) = 3 + sinxsiny. Given a point (a, b) in the domain of f, the maximum value of the directional derivative at that point is given by ‖ ⇀ ∇ f(a, b)‖. This would equal the rate of greatest ascent if the surface represented a topographical map.Definition 1.3.1. The circle which best approximates a given curve near a given point is called the circle of curvature or the osculating circle 2 at the point. The radius of the circle of curvature is called the radius of curvature at the point and is normally denoted ρ. The curvature at the point is κ = 1 ρ.the tangent planes of uncorrupted surfaces cannot be esti-mated. In our method, tangent plane T (S) on superpixel S is used as a 2D plane that has finite width in 3D space. The center c(S) of the tangent plane is the center of point cloud d(S) that is defined by locally upsampled depth informa-tion on superpixel S. The tangent plane is ...Many of our calculators provide detailed, step-by-step solutions. This will help you better understand the concepts that interest you. eMathHelp: free math calculator - solves algebra, geometry, calculus, statistics, linear algebra, and linear programming problems step by step.in the plane using osculating circles and local approximation by parabolas. 2.3.3 Definitions as bending of tangent in arclength; alternate forms. Eventually Newton’s definition was refined to become the geometric version used today, which says: Along a curve, measure the instantaneous rate at which theWe do this by starting at (x0, f(x0)) ( x 0, f ( x 0)) and moving along the tangent line to approximate the value of the function at x x . Look at f(x) = arctanx f ( x) = arctan x. Let’s use the tangent approximation f(x) ≈ f(x0) +f′(x0)(x −x0) f ( x) ≈ f ( x 0) + f ′ ( x 0) ( x − x 0) to approximate f(1.04) f ( 1.04) :Solution. Find the linear approximation to z =4x2 −ye2x+y z = 4 x 2 − y e 2 x + y at (−2,4) ( − 2, 4). Solution. Here is a set of practice problems to accompany the Tangent Planes and Linear Approximations section of the Applications of Partial Derivatives chapter of the notes for Paul Dawkins Calculus III course at Lamar University.What is the Tangent Plane?, cont. Note that the lines T 1 and T 2 generate a unique plane that contains them both: This is the plane tangent to S at the point P, i.e., the tangent plane at P, so called because it contains the two tangent lines. Note that it, too lies tangent to S. Toward an Equation The tangent line calculator finds the equation of the tangent line to a given curve at a given point. Step 2: Click the blue arrow to submit. Choose "Find the Tangent Line at the Point" from the topic selector and click to see the result in our Calculus Calculator ! Examples . Find the Tangent Line at (1,0) Popular Problems Example. A military plane takes o from a military base. Its trajectory is a parabolic curve y= 2000x x2. At the point with coordinates (1200;960000) the plane launches a missile towards the target with the coordinates (1800;720000). The path of the missile is a straight line tangent to the trajectory of the plane at the point of the launch. Find the Linear Approximation to. We are just asking for the equation of the tangent plane: Step 2: Take the partial derivative of with respect with (x,y): Step 3: Evaluate the partial derivative of x at Step 4: Take the partial derivative of Step 5: Evaluate the partial derivative at. Step 6: Convert (x,y) back into binomials: Step 7: Write ... Dec 18, 2020 · Furthermore the plane that is used to find the linear approximation is also the tangent plane to the surface at the point (x0, y0). Figure 2.5.5: Using a tangent plane for linear approximation at a point. Given the function f(x, y) = √41 − 4x2 − y2, approximate f(2.1, 2.9) using point (2, 3) for (x0, y0). Furthermore the plane that is used to find the linear approximation is also the tangent plane to the surface at the point (x 0, y 0). ( x 0 , y 0 ) . Figure 4.31 Using a tangent plane for linear approximation at a point. The tangent line calculator finds the equation of the tangent line to a given curve at a given point. Step 2: Click the blue arrow to submit. Choose "Find the Tangent Line at the Point" from the topic selector and click to see the result in our Calculus Calculator ! Examples . Find the Tangent Line at (1,0) Popular ProblemsIn exercises 8 - 19, find the equation for the tangent plane to the surface at the indicated point. ... Use the differential \( dz\) to approximate the change in \( z=\sqrt{4−x^2−y^2}\) …f(x, y) ≈ 4x + 2y – 3 is called the linear approximation or tangent plane approximation of f at (1, 1). LINEAR APPROXIMATIONS. For instance, at the point (1.1, ...Nov 10, 2020 · When working with a function of two variables, the tangent line is replaced by a tangent plane, but the approximation idea is much the same. Definition: Linear Approximation Given a function \( z=f(x,y)\) with continuous partial derivatives that exist at the point \( (x_0,y_0)\), the linear approximation of \(f\) at the point \( (x_0,y_0)\) is ... A free online 2D graphing calculator (plotter), or curve calculator, that can plot piecewise, linear, quadratic, cubic, quartic, polynomial, trigonometric, hyperbolic, exponential, logarithmic, inverse functions given in different forms: explicit, implicit, polar, and parametric. It can also graph conic sections, arbitrary inequalities or ... Your question might be in a wrong page, an equation for f(x,y) and a specific coordinate are needed to calculate the tangent plane. Comment Button navigates to signup page (1 vote) Upvote. Button navigates to signup page. Downvote. Button navigates to signup page. ... I need to find the tangent plane to the surface at the point P(π/3, 2).Final answer. Use the tangent plane approximation to calculate approximately how much more area a rectangle that is 5.01 by 3.02 cm has than one which is 5 by 3 . Draw a diagram showing the smaller rectangle inside the enlarged rectangle. On this diagram clearly indicate rectangles corresponding to the two terms in the tangent line approximation.This means that the equation of the tangent plane is $ z – 2 = -4(x + 2) – 2(y – 1)$ or $ z = -4x – 2y -4$. Linear Approximation: Application of Tangent Planes. Through tangent planes, we can now approximate the linearization of functions. Notice how the resulting tangent plane returns a linear equation? Jan 26, 2022 · First, let’s recall that we could approximate a point by its tangent line in single variable calculus. y − y 0 = f ′ ( x 0) ( x − x 0) x. This point-slope form of the tangent line is the linear approximation, or linearization, of f ( x) at the point ( x 0, y 0). Now, let’s extend this idea for a function of two variables. tangent plane to z=2xy^2-x^2y at (x,y)=(3,2) Natural Language; Math Input; Extended Keyboard Examples Upload Random. Compute answers using Wolfram's breakthrough …Drag P P along the parabola or enter the x-coordinate for point P P . Notice how the equation of the tangent line changes as you move point P P . What happens when x = 0 x = 0 for this function? What about as |x| | x | gets large? Now that we can find the tangent to a curve at a point, of what use is this?How the Calculator Works Tangent Plane Lesson What is a Tangent Plane? A tangent plane is a plane that is tangent to a smooth surface (characterized by a differentiable function f ) at a specified point. Figure 1 - Plane Tangent to Surface at Point ( x0, y0, z0) Figure 2 - Side View of Plane Tangent to Surface at Point ( x0, y0, z0)Tangent Plane. Determine the plane touching a surface at a given point. Tangential Component of Acceleration. Measure acceleration in the direction of motion. Taylor …Tangent Plane & Linear Approximations w/ Step-by-Step Examples! // Last Updated: January 26, 2022 - Watch Video // How to find a tangent plane? Jenn, Founder Calcworkshop ®, 15+ Years Experience (Licensed & Certified Teacher) And why would we want to? Because of all the functions to work with, linear functions are the easiest.Furthermore the plane that is used to find the linear approximation is also the tangent plane to the surface at the point (x0, y0). Figure 14.4.5: Using a tangent plane for linear approximation at a point. Given the function f(x, y) = √41 − 4x2 − y2, approximate f(2.1, 2.9) using point (2, 3) for (x0, y0).Free linear algebra calculator - solve matrix and vector operations step-by-step ... Integral Applications Integral Approximation Series ODE Multivariable Calculus ...The output value of L together with its input values determine the plane. The concept is similar to any single variable function that determines a curve in an x-y plane. For example, f (x)=x^2 determines a parabola in an x-y plane even though f (x) outputs a scalar value. BTW, the topic of the video is Tangent Planes of Graphs. Here is a set of notes used by Paul Dawkins to teach his Calculus III course at Lamar University. Topics covered are Three Dimensional Space, Limits of functions of multiple variables, Partial Derivatives, Directional Derivatives, Identifying Relative and Absolute Extrema of functions of multiple variables, Lagrange Multipliers, Double …The output value of L together with its input values determine the plane. The concept is similar to any single variable function that determines a curve in an x-y plane. For example, f (x)=x^2 determines a parabola in an x-y plane even though f (x) outputs a scalar value. BTW, the topic of the video is Tangent Planes of Graphs. Explore math with our beautiful, free online graphing calculator. Graph functions, plot points, visualize algebraic equations, add sliders, animate graphs, and more. Tangent Line Calculator. Save Copy. Log InorSign Up. f x = x 3. 1. a, b. 2. d da f a x − a + f a = y. 3. a = − 0. 3 9. 4. b = f a. 5. d ...The electrical load of a home basically tells you how much electricity your home is using. This is an approximation of your usage, not an exact number. The exact amount can only be determined through metering your electric, which is what ...tangent line calculator. Natural Language. Math Input. Extended Keyboard. Examples. Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.Dec 18, 2020 · Furthermore the plane that is used to find the linear approximation is also the tangent plane to the surface at the point (x0, y0). Figure 2.5.5: Using a tangent plane for linear approximation at a point. Given the function f(x, y) = √41 − 4x2 − y2, approximate f(2.1, 2.9) using point (2, 3) for (x0, y0). The output value of L together with its input values determine the plane. The concept is similar to any single variable function that determines a curve in an x-y plane. For example, f (x)=x^2 determines a parabola in an x-y plane even though f (x) outputs a scalar value. BTW, the topic of the video is Tangent Planes of Graphs. Find the Linear Approximation to. We are just asking for the equation of the tangent plane: Step 2: Take the partial derivative of with respect with (x,y): Step 3: Evaluate the partial derivative of x at Step 4: Take the partial derivative of Step 5: Evaluate the partial derivative at. Step 6: Convert (x,y) back into binomials: Step 7: Write ... Free normal line calculator ... System of Inequalities Polynomials Rationales Complex Numbers Polar/Cartesian Functions Arithmetic & Comp. Coordinate Geometry Plane Geometry Solid Geometry Conic Sections Trigonometry. ... Tangent to Conic; Linear Approximation; Difference Quotient; Horizontal Tangent; Limits. One Variable; Multi …Since the equation of the tangent plane at (a,b,f(a,b)) is z = f(a,b)+(x−a) ... The function L(x,y) is also called the Linear Approximation to f at (a,b).
Example. A military plane takes o from a military base. Its trajectory is a parabolic curve y= 2000x x2. At the point with coordinates (1200;960000) the plane launches a missile towards the target with the coordinates (1800;720000). The path of the missile is a straight line tangent to the trajectory of the plane at the point of the launch.. 16 inch drop bedskirt king
Figure 3.5.4: Linear approximation of a function in one variable. The tangent line can be used as an approximation to the function f(x) for values of x reasonably close to x = a. When working with a function of two variables, the tangent line is replaced by a tangent plane, but the approximation idea is much the same.Free tangent line calculator - find the equation of the tangent line given a point or the intercept step-by-step What is the Tangent Plane?, cont. Note that the lines T 1 and T 2 generate a unique plane that contains them both: This is the plane tangent to S at the point P, i.e., the tangent plane at P, so called because it contains the two tangent lines. Note that it, too lies tangent to S. Toward an EquationTo improve enhancement accuracy, we use local tangent planes as local coordinates for the measured surfaces. Our method is composed of two steps, a calculation ...Explore math with our beautiful, free online graphing calculator. Graph functions, plot points, visualize algebraic equations, add sliders, animate graphs, and more. Tangent Line Approximation | Desmos A calculator gives an estimate of 0.8187307531 for the value of \displaystyle{ \dfrac ... Find an equation of the tangent plane to the graph of f(x,y) = x/x+y at the point (2,7). (b) Write the linear approximation at (2,7) (c) ... The tangent line approximation \, L(x)\, is the best first-degree (linear) approximation to \, f(x)\, ...This problem has been solved! You'll get a detailed solution from a subject matter expert that helps you learn core concepts. Question: Cooper 15.3.01 Apply the tangent plane approximation to find f (2.003, 1.04) where f (x, y) = 3x² + y2. f (2.003, 1.04) Online Math Lab resources for this problem: . Multivariable Calculus.Use the linear approximation to calculate $(-1.99, 4.01)$. Solution. As we have learned in our discussion, we can use the tangent plane to form the linear approximate of the curve. This means that we’ll first find the equation representing the tangent plane, so let’s go ahead and evaluate the partial derivatives of the function.A) Find the plane tangent to the graph of the function in P = (2, 0) and calculate the linear approximation of the function in (1.9, 0.1). B) Find the dire Find the equation for a plane which is tangent to the graph of the function f(x,y) = x^3 + 3x^2y - y^2 - …An exact derivation of the Scherrer equation is given for particles of spherical shape, values of the constant for half-value breadth and for integral breadth being obtained. Various approximation methods which have been used are compared with the exact calculation. The tangent plane approximation of v. Laue is shown to be quite satisfactory, but some …Jun 14, 2019 · Furthermore the plane that is used to find the linear approximation is also the tangent plane to the surface at the point (x0, y0). Figure 5: Using a tangent plane for linear approximation at a point. Given the function f(x, y) = √41 − 4x2 − y2, approximate f(2.1, 2.9) using point (2, 3) for (x0, y0). CosY = 0.30. This is where the Inverse Functions come in. If we know that CosY = 0.30, we're trying to find the angle Y that has a Cosine 0.30. To do so: -Enter 0.30 on your calculator. -Find the Inverse button, then the Cosine button (This could also be the Second Function button, or the Arccosine button).Therefore, the tangent line gives us a fairly good approximation of [latex]f(2.1)[/latex] (Figure 1b). However, note that for values of [latex]x[/latex] far from 2, the equation of the tangent line does not give us a good approximation. For example, if [latex]x=10[/latex], the [latex]y[/latex]-value of the corresponding point on the tangent line isFree tangent line calculator - find the equation of the tangent line given a point or the intercept step-by-stepThe tangent line calculator finds the equation of the tangent line to a given curve at a given point. Step 2: Click the blue arrow to submit. Choose "Find the Tangent Line at the Point" from the topic selector and click to see the result in our Calculus Calculator ! Examples . Find the Tangent Line at (1,0) Popular Problems Send us Feedback. Free Multivariable Calculus calculator - calculate multivariable limits, integrals, gradients and much more step-by-step.Find an approximate value for \(f (-0.9\,,\, 1.1)\) without using a calculator or computer. 5. Four numbers, each at least zero and each at most 50, are rounded to the first decimal place and then multiplied together. ... Find the tangent plane approximation to the value of \(f(1.99, 1.01)\) using the tangent plane from part (a). 25.Jan 26, 2022 · First, let’s recall that we could approximate a point by its tangent line in single variable calculus. y − y 0 = f ′ ( x 0) ( x − x 0) x. This point-slope form of the tangent line is the linear approximation, or linearization, of f ( x) at the point ( x 0, y 0). Now, let’s extend this idea for a function of two variables. Then the plane that contains both tangent lines T 1 and T 2 is called the tangent plane to the surface S at the point P. Equation of Tangent Plane: An equation of the tangent plane to the surface z = f(x;y) at the point P(x 0;y 0;z 0) is z z 0 = f x(x 0;y 0)(x x 0) + f y(x 0;y 0)(y y 0) Note how this is similar to the equation of a tangent line..