Problem 27 - College Algebra and Calculus: An Applied Approach

Question

In Exercises, find the second derivative. $$ f(x)=2 e^{3 x}+3 e^{-2 x} $$

Step-by-Step Solution

Answer

The second derivative of the given function \(f(x)=2 e^{3x}+3 e^{-2x}\) is \(f''(x)=18e^{3x}-12e^{-2x}\).

Step 1: Calculate the First Derivative

Firstly, apply the chain rule to obtain the derivative of the given function \(f(x)=2 e^{3x}+3 e^{-2x}\). The chain rule states that the derivative of a composite function is the derivative of the outer function times the derivative of the inner function. The derivative of a function \(e^{u}\) is \(u' e^{u}\) and the derivative of \(2e^{3x}\) is \(6e^{3x}\) and of \(3e^{-2x}\) is \(-6e^{-2x}\). Hence the first derivative \(f'(x)\) of the function is \(f'(x)=6e^{3x}-6e^{-2x}.\)

Step 2: Calculate the Second Derivative

Having computed the first derivative, we use it to find the second derivative \(f''(x)\). Apply the chain rule again to the first derivative, yielding \(f''(x)=18e^{3x}-12e^{-2x}.\)

Key Concepts

Chain Rule

Understanding the chain rule in calculus is essential for dealing with composite functions—functions made up of two or more other functions. Imagine you are wearing a set of nested dolls, each layer representing a function, and you're gradually peeling them off to reach the core. That's essentially what the chain rule helps with in differentiation.

When you're given a composite function, like an exponential function that has a variable in its exponent, the chain rule tells you to take the derivative of the outer function (in our case, the exponential part), and then multiply it by the derivative of the inner function (the part inside the exponent). Consider the given function from the exercise:

• The outer function is the exponential function, e.g., \(e^{3x}\).
• The inner function is the actual exponent, the \(3x\) part.

You first differentiate \(e^{3x}\) as though the 3x were a constant, which gives \(e^{3x}\), and then multiply it by the derivative of \(3x\), which is 3. Therefore, the derivative of \(2e^{3x}\) simplifies to \(6e^{3x}\). This process is repeated for each term in the function that requires application of the chain rule.

Exponential Functions

Exponential functions, like \(e^x\), are found frequently in calculus problems. These functions are unique because the rate of growth is proportional to the value of the function itself. The base of the exponential function e, approximately equal to 2.71828, is the base rate of growth shared by all continually growing processes.

The derivative of an exponential function is notable because it results in a very similar function to the original. Specifically, the derivative of \(e^u\), where u is a function of x, is \(u'e^u\). This reflects the unchanged growth rate as the output increases. The exercise solution leverages this by differentiating \(e^{3x}\) to get \(3e^{3x}\), and \(e^{-2x}\) accordingly to yield \(-2e^{-2x}\), taking into account the chain rule to incorporate the relevant multiplication by the derivatives of the powers.

First Derivative

The first derivative of a function is, simply put, the equation that tells us the slope or rate of change of the original function at any point. It's the speedometer of calculus; just as a speedometer tells you how fast you're going at an instant in a car, the first derivative tells you how fast the y-value of a function is changing at any instant of x.

For the function in the exercise, the first derivative \(f'(x)\) was calculated as \(6e^{3x} - 6e^{-2x}\). This result informs us about the increasing and decreasing behavior of the function \(f(x)\) at any point. If you plot both \(f(x)\) and \(f'(x)\) on a graph, \(f'(x)\) will show the gradient of the slope at each point along \(f(x)\). Knowing the first derivative is crucial because it sets the foundation for finding the second derivative, which then speaks about the acceleration of the function—how the slope itself is changing.