Chapter 3: Problem 95
Find and simplify \(\frac{d^{2}}{d x^{2}}\left(\frac{f(x)}{g(x)}\right)\) using the product and chain rules.
Short Answer
Expert verified
The second derivative is \( \frac{(g(x))^2(u') - u(2g(x)g'(x))}{(g(x))^4} \).
Step by step solution
01
Identify the Quotient Rule
The derivative of a quotient \( \frac{f(x)}{g(x)} \) can be found using the quotient rule, which is \( \frac{d}{dx}\left(\frac{f(x)}{g(x)}\right) = \frac{g(x)f'(x) - f(x)g'(x)}{(g(x))^2} \). We will use this to find the first derivative.
02
Differentiate According to the Quotient Rule
Find the first derivative \( \frac{d}{dx} \left( \frac{f(x)}{g(x)} \right) \). Using the formula from the quotient rule: \[ \frac{d}{dx} \left( \frac{f(x)}{g(x)} \right) = \frac{g(x)f'(x) - f(x)g'(x)}{(g(x))^2} \]
03
Differentiate the Result Using the Quotient Rule Again
Now, take the derivative of the result from Step 2. Apply the quotient rule to \( \frac{g(x)f'(x) - f(x)g'(x)}{(g(x))^2} \). Let \( u = g(x)f'(x) - f(x)g'(x) \) and \( v = (g(x))^2 \). The second derivative is:\[ \frac{d^2}{dx^2} \left( \frac{f(x)}{g(x)} \right) = \frac{v \cdot u' - u \cdot v'}{v^2} \]
04
Calculate Derivatives of u and v
Calculate \( u' = \frac{d}{dx}(g(x)f'(x) - f(x)g'(x)) \) which uses the product rule for differentiation, and \( v' = \frac{d}{dx}((g(x))^2) \). \\( u' = g(x)f''(x) + g'(x)f'(x) - (f'(x)g'(x) + f(x)g''(x)) \)\( v' = 2g(x)g'(x) \)
05
Substitute and Simplify
Substitute the values of \( u' \) and \( v' \) into the formula from Step 3. This results in: \[ \frac{d^2}{dx^2} \left( \frac{f(x)}{g(x)} \right) = \frac{(g(x))^2(u') - (g(x)f'(x) - f(x)g'(x))(2g(x)g'(x))}{(g(x))^4} \]Simplify the expression where possible.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Quotient Rule
The quotient rule is a technique used to differentiate functions that are ratios of two differentiable functions. Specifically, if you have a function given by \( \frac{f(x)}{g(x)} \), the derivative is computed using the formula:
- \( \frac{d}{dx}\left(\frac{f(x)}{g(x)}\right) = \frac{g(x)f'(x) - f(x)g'(x)}{(g(x))^2} \)
Product Rule
The product rule is another fundamental rule in differentiation used when you need to differentiate the product of two functions. Although the original function \( \frac{f(x)}{g(x)} \) is a quotient, the product rule becomes relevant when differentiating components like \( g(x)f'(x) \) or \( f(x)g'(x) \). The product rule is expressed as:
- For functions \( u(x) \) and \( v(x) \), the derivative of their product \( uv \) is \( u'v + uv' \).
Chain Rule
The chain rule is pivotal for finding the derivative of compositions of functions. It is used when a function is applied within another function, like \( h(x) = f(g(x)) \). Although the original exercise does not explicitly list a composite function, the chain rule's concept simplifies parts of derivatives embedded within the derivatives you calculate using the quotient and product rules. Formally, if \( y = f(g(x)) \), the chain rule states:
- \( \frac{dy}{dx} = f'(g(x)) \cdot g'(x) \).
Differentiation Techniques
Differentiation involves various techniques to systematically find derivatives, enabling you to understand how a function changes at any point. Key techniques include the quotient, product, and chain rules—each indispensable for different function types.
- Quotient Rule: Used for differentiating ratios.
- Product Rule: Applied for products of two functions.
- Chain Rule: Essential for function compositions.