Chapter 4: Problem 56
Find the second derivative of each function. $$ f(x)=e^{-x^{6} / 6} $$
Short Answer
Expert verified
The second derivative is \( f''(x) = e^{-x^6 / 6} (x^{10} - 5x^4) \).
Step by step solution
01
Find the First Derivative
To find the first derivative of the function, we use the chain rule. The function is given by \( f(x) = e^{-x^6 / 6} \). Let \( u = -x^6 / 6 \), so \( f(x) = e^u \). Then, \( \frac{du}{dx} = -x^5 \) and the first derivative is: \( f'(x) = e^u \cdot \frac{du}{dx} = e^{-x^6 / 6} \cdot (-x^5) \). Therefore, \( f'(x) = -x^5 e^{-x^6 / 6} \).
02
Find the Second Derivative
To find the second derivative, we need to differentiate the first derivative \( f'(x) = -x^5 e^{-x^6 / 6} \). Again, we use the product rule and chain rule. For \( u = -x^6 / 6 \) and \( v = -x^5 \), we have: \( \frac{du}{dx} = -x^5 \) and \( \frac{dv}{dx} = -5x^4 \). The product rule gives: \( f''(x) = \left( \frac{dv}{dx} \cdot e^u + v \cdot e^u \cdot \frac{du}{dx} \right) \). Substitute to get: \( f''(x) = (-5x^4)e^{-x^6 / 6} + (-x^5)(e^{-x^6 / 6})(-x^5) \). Simplifying, \( f''(x) = -5x^4 e^{-x^6 / 6} + x^{10} e^{-x^6 / 6} \). Therefore, \( f''(x) = e^{-x^6 / 6} (x^{10} - 5x^4) \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Chain Rule
The chain rule is a fundamental differentiation technique used when dealing with composite functions. Essentially, it helps us find the derivative of a function that is nested within another function. For instance, consider our function \( f(x) = e^{-x^6 / 6} \). Here, the exponent \(-x^6 / 6\) can be viewed as a function of \(x\), let's call it \(u\).
- In this scenario, \( f(x) = e^u \) and \( u = -x^6 / 6 \).
- First, we differentiate \( u \) with respect to \( x \), giving us \( \frac{du}{dx} = -x^5 \).
- Then, the chain rule states that the derivative of \( f \) with respect to \( x \), is given by \( \frac{df}{du} \cdot \frac{du}{dx} \).
Product Rule
When you need to differentiate a product of two functions, the product rule comes into play. It's particularly handy when each part of the expression can itself be a product of different functions. Let's look at the first derivative we found: \( f'(x) = -x^5 e^{-x^6 / 6} \).
- Here, we have two functions of \(x\): \( v = -x^5 \) and \( u = e^{-x^6 / 6} \).
- The product rule tells us that the derivative of the product is \( \frac{dv}{dx} \cdot u + v \cdot \frac{du}{dx} \).
- First, find \( \frac{dv}{dx} = -5x^4 \).
Differentiation Techniques
Differentiation is the process of finding the derivative of a function, which is essential for understanding how functions change. The techniques used in differentiation, like the chain rule and product rule, serve different purposes depending on the problem.
- Each technique is structured to handle specific forms of function equally smoothly.
- The chain rule is best for nested functions, where we unravel the layers step by step.
- The product rule is specifically tailored for cases where two functions multiply.