Textbook Question
9–61. Evaluate and simplify y'.
y = tan^−1 √t²−1
6. Derivatives of Inverse, Exponential, & Logarithmic Functions
Derivatives of Inverse Trigonometric Functions
7:00 minutesProblem 3.R.87
Textbook Question
Consider the following functions. In each case, without finding the inverse, evaluate the derivative of the inverse at the given point.
y =√x³+x−1 at y=3
Verified step by step guidance1
First, understand that if y = f(x), then the inverse function is x = f^(-1)(y). The derivative of the inverse function at a point y = a is given by the formula: (f^(-1))'(a) = 1 / f'(x), where x is such that f(x) = a.
Given the function y = √(x³ + x − 1), we need to find the value of x such that y = 3. This means solving the equation √(x³ + x − 1) = 3 for x.
Square both sides of the equation to eliminate the square root: (x³ + x − 1) = 9. Simplify this to x³ + x − 10 = 0. Solve this equation to find the value of x.
Once you have the value of x, compute the derivative of the original function y = √(x³ + x − 1) with respect to x. Use the chain rule: if y = u^(1/2), then dy/dx = (1/2)u^(-1/2) * du/dx, where u = x³ + x − 1.
Finally, evaluate the derivative at the found x value and use the formula for the derivative of the inverse: (f^(-1))'(3) = 1 / f'(x). This will give you the derivative of the inverse function at y = 3.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Inverse Function Theorem
The Inverse Function Theorem states that if a function is continuous and differentiable, and its derivative is non-zero at a point, then the function has a locally defined inverse around that point. The derivative of the inverse function at a point can be found using the formula: (dy/dx)⁻¹ = 1/(dy/dx) evaluated at the corresponding point.
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Derivative of a Function
The derivative of a function measures the rate at which the function's value changes as its input changes. It is defined as the limit of the average rate of change of the function over an interval as the interval approaches zero. For the function y = √(x³ + x - 1), finding the derivative involves applying rules of differentiation such as the power rule and the chain rule.
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Evaluating Derivatives at Specific Points
To evaluate the derivative at a specific point, one must first find the derivative function and then substitute the x-value that corresponds to the given y-value. In this case, we need to determine the x-value for which y = 3, and then use that x-value to compute the derivative, which will help in finding the derivative of the inverse function at that point.
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