Skip to main content
Ch. 3 - Derivatives
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Not the one you use?Change textbook
All textbooksBriggs 3rd EditionCh. 3 - DerivativesProblem 3.10.86c
Chapter 3, Problem 3.10.86c

Tangents and inverses Suppose L(x)=ax+b (with a≠0) is the equation of the line tangent to the graph of a one-to-one function f at (x0,y0). Also, suppose M(x)=cx+d is the equation of the line tangent to the graph of f^−1 at (y0,x0).


c. Prove that L^−1(x)=M(x).

Verified step by step guidance
1
Start by understanding the relationship between a function and its inverse. If L(x) is tangent to f at (x0, y0), then the slope of L(x), which is 'a', is equal to the derivative of f at x0, i.e., f'(x0) = a.
For the inverse function f^−1, the derivative at a point (y0, x0) is the reciprocal of the derivative of f at x0. Therefore, the slope of M(x), which is 'c', is equal to 1/a, i.e., c = 1/a.
The line L(x) = ax + b is tangent to f at (x0, y0), so it passes through the point (x0, y0). Therefore, y0 = ax0 + b, which can be rearranged to find b: b = y0 - ax0.
Similarly, the line M(x) = cx + d is tangent to f^−1 at (y0, x0), so it passes through the point (y0, x0). Therefore, x0 = cy0 + d, which can be rearranged to find d: d = x0 - cy0.
To prove L^−1(x) = M(x), find the inverse of L(x). The inverse L^−1(x) is found by swapping x and y in the equation y = ax + b and solving for y. This gives L^−1(x) = (x - b)/a. Substitute b = y0 - ax0 into this equation to show that L^−1(x) = M(x) = (1/a)x + (x0 - (1/a)y0).

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
3m
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Inverse Functions

An inverse function essentially reverses the effect of the original function. If f(x) takes an input x and produces an output y, then the inverse function f^−1(y) takes y back to x. For a function to have an inverse, it must be one-to-one, meaning each output is produced by exactly one input.
Recommended video:
4:49
Inverse Cosine

Tangent Lines

A tangent line to a function at a given point represents the instantaneous rate of change of the function at that point. The slope of the tangent line is given by the derivative of the function at that point. In the context of the problem, the tangent lines L(x) and M(x) represent the slopes of the original function f and its inverse f^−1, respectively.
Recommended video:
05:13
Slopes of Tangent Lines

Properties of Derivatives

The derivative of a function at a point provides information about the function's behavior near that point, including its slope. For inverse functions, a key property is that the slopes of the tangent lines at corresponding points are reciprocals of each other. This relationship is crucial for proving that the inverse of the tangent line L(x) equals the tangent line M(x).
Recommended video:
06:21
Properties of Functions
Related Practice
Textbook Question

62–65. {Use of Tech} Graphing f and f'

c. Verify that the zeros of f' correspond to points at which f has a horizontal tangent line.

f(x)=(x²−1)sin^−1 x on [−1,1]

Textbook Question

Airline travel The following figure shows the position function of an airliner on an out-and-back trip from Seattle to Minneapolis, where s = f(t) is the number of ground miles from Seattle t hours after take-off at 6:00 A.M. The plane returns to Seattle 8.5 hours later at 2:30 P.M. <IMAGE>

d. Determine the velocity of the airliner at noon (t = 6) and explain why the velocity is negative.

Textbook Question

Highway travel A state patrol station is located on a straight north-south freeway. A patrol car leaves the station at 9:00 A.M. heading north with position function s = f(t) that gives its location in miles t hours after 9:00 A.M. (see figure). Assume s is positive when the car is north of the patrol station. <IMAGE>

c. Find the average velocity of the car over the interval [1.75, 2.25]. Estimate the velocity of the car at 11:00 A.M. and determine the direction in which the patrol car is moving.

Textbook Question

{Use of Tech} Flow from a tank A cylindrical tank is full at time t=0 when a valve in the bottom of the tank is opened. By Torricelli’s law, the volume of water in the tank after t hours is V=100(200−t)², measured in cubic meters.

d. At what time is the magnitude of the flow rate a minimum? A maximum?  

Textbook Question

Explain why or why not Determine whether the following statements are true and give an explanation or counterexample.

d. The lines tangent to the graph of y=sin x on the interval [−π/2,π/2] have a maximum slope of 1.

Textbook Question

Finding derivatives from a table Find the values of the following derivatives using the table. <IMAGE>


c. d/dx ((f(x)g(x)) |x=3

1
views