Question

If \(F(x)=\int_{x^{2}}^{e^{x}} \cos t \quad d t\), find \(F^{\prime}(x)\)

Short answer

Question: Find the derivative of \(F(x) = \int_{x^2}^{e^x} cos(t) dt\) with respect to x. Answer: \(F'(x) = \cos(e^x)e^x - \cos(x^2)2x\)

Step-by-step solution

Find the derivatives of a(x) and b(x) with respect to x

First, find the derivatives of \(a(x) = x^2\) and \(b(x) = e^x\) with respect to x. Using the power rule, the derivative of \(a(x)\) is: $$ a'(x) = \frac{d}{dx}(x^2) = 2x $$ Since \(e^x\) is an exponential function, its derivative with respect to x is: $$ b'(x) = \frac{d}{dx}(e^x) = e^x $$

Calculate the derivative of F(x) using the Fundamental theorem of calculus

Now that we have \(a'(x)\) and \(b'(x)\), substitute the values into the formula from the Fundamental theorem of calculus part 1: $$ F'(x) = g(b(x))b'(x) - g(a(x))a'(x) = \cos(e^x)e^x - \cos(x^2)2x $$

Write the final answer

The derivative of F(x) with respect to x is: $$ F'(x) = \cos(e^x)e^x - \cos(x^2)2x $$ This is the final answer.

Key concepts

Fundamental Theorem of Calculus

Understanding the connection between differentiation and integration is crucial for calculus students, and the Fundamental Theorem of Calculus (FTC) beautifully reveals this relationship. The FTC consists of two parts, and for our current problem, the first part is particularly useful. It states that if you have a continuous function over an interval and you create a new function by integrating the original function over a variable limit, the derivative of this new function is just the original function evaluated at the upper limit of integration.

Applied to the given exercise, where the function being integrated, \( \cos t \), is continuous, and the variable limits of integration are \( x^2 \) and \( e^x \), the FTC simplifies the process of finding \( F'(x) \) by allowing us to differentiate the upper and lower bounds separately rather than integrating and then differentiating the whole function. Such a direct linkage between the derivative and the antiderivative is what makes the FTC a cornerstone of calculus.

Chain Rule in Differentiation

Whenever a function is composed of multiple layers or nested functions, the chain rule is the tool we use in differentiation. The rule states that to find the derivative of a composite function, you differentiate the outer function and multiply it by the derivative of the inner function. This process continues until all nested layers have been differentiated.

In terms of our exercise, the chain rule comes into play when determining the derivatives of the upper and lower limits of the integral, which are functions themselves (\( b(x) = e^x \) and \( a(x) = x^2 \) respectively). Here, although the outer functions (exponential and power functions) are relatively straightforward, applying the chain rule correctly is pivotal in leading to the accurate final differentiation of \( F(x) \). For students, understanding each 'link' in this 'chain' of derivatives is fundamental for solving problems involving derivatives of integrals with variable limits.

Differentiation of Exponential Functions

Exponential functions, such as \( e^x \), are unique in that they are the only type of function whose derivative is the same as the function itself. This characteristic is one of the reasons why exponential functions appear so frequently in various fields, including growth processes, physics, and finance.

To demonstrate this in our textbook exercise, we differentiate the upper limit of the integral, \( b(x) = e^x \), to get \( b'(x) = e^x \). It may seem counterintuitive at first that a function's rate of change at any point is exactly equal to the value of the function at that point, but this is a powerful property that significantly eases the process when working with derivatives of exponential functions. For students, becoming comfortable with this concept opens the door to solving more complex problems involving exponential growth and decay.