Chapter 2: Problem 32
Evaluate the indicated derivative. \(g^{\prime}\left(\frac{1}{2}\right)\) if \(g(s)=\cos \pi s \sin ^{2} \pi s\)
Short Answer
Expert verified
The derivative \( g'\left( \frac{1}{2} \right) \) is \(-\pi\).
Step by step solution
01
Identify the Function to Differentiate
The function we want to take the derivative of is given by \( g(s) = \cos(\pi s) \sin^2(\pi s) \). We are asked to find \( g'\left( \frac{1}{2} \right) \).
02
Use the Product Rule
To differentiate \( g(s) \), apply the product rule for the function \( u(s) = \cos(\pi s) \) and \( v(s) = \sin^2(\pi s) \). The product rule is \( (uv)' = u'v + uv' \).
03
Differentiate \( u(s) = \cos(\pi s) \)
The derivative \( u'(s) \) is \( -\pi \sin(\pi s) \) because the derivative of \( \cos(x) \) is \( -\sin(x) \), and we use the chain rule since the argument is \( \pi s \).
04
Differentiate \( v(s) = \sin^2(\pi s) \) using the Chain Rule
Rewrite \( v(s) \) as \( (\sin(\pi s))^2 \). Using the chain rule, let \( w(t) = t^2 \) and \( t = \sin(\pi s) \), so \( v'(s) = 2 \cdot \sin(\pi s) \cdot \pi \cos(\pi s) \).
05
Substitute the Derivatives Into the Product Rule Formula
Substitute \( u'(s) \) and \( v'(s) \) into the product rule formula: \[g'(s) = (-\pi \sin(\pi s))\sin^2(\pi s) + \cos(\pi s)(2\sin(\pi s) \cdot \pi \cos(\pi s)).\]
06
Simplify the Expression
Simplify the expression: \[g'(s) = -\pi \sin(\pi s) \cdot \sin(\pi s) \cdot \sin(\pi s) + 2\pi \cos^2(\pi s) \cdot \sin(\pi s).\]Rewrite the first term as \( -\pi \sin^3(\pi s) \) and the second term as \( 2\pi \sin(\pi s) \cos^2(\pi s) \).
07
Evaluate the Derivative at \( s = \frac{1}{2} \)
Substitute \( s = \frac{1}{2} \): \[g'\left( \frac{1}{2} \right) = -\pi \sin^3\left(\frac{\pi}{2}\right) + 2\pi \sin\left( \frac{\pi}{2} \right) \cos^2\left( \frac{\pi}{2} \right).\]Since \( \sin\left( \frac{\pi}{2} \right) = 1 \) and \( \cos\left( \frac{\pi}{2} \right) = 0 \), the expression simplifies to \( -\pi \).
08
Simplify to Get the Final Result
After substituting and simplifying, the derivative at \( s = \frac{1}{2} \) is:\[g'\left( \frac{1}{2} \right) = -\pi.\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Product Rule
A key technique in calculus for differentiating two multiplied functions is the Product Rule. It's extraordinarily helpful when confronted with a function that is the product of two separate functions. The rule is stated as: if you have two functions, say, \( u(x) \) and \( v(x) \), then the derivative of their product \( uv \) is calculated as \((uv)' = u'v + uv'\). This means that to differentiate \( uv \), you need to find the derivative of \( u \) and multiply it by \( v \), then add it to the product of \( u \) and the derivative of \( v \). This rule is a cornerstone of differentiation techniques and makes handling complex products straightforward.
Chain Rule
The Chain Rule is an essential differentiation technique used when dealing with composite functions—functions within functions. Consider a function \( f(g(x)) \), where \( g \) is wrapped in \( f \). The Chain Rule states that the derivative of \( f(g(x)) \) is \( f'(g(x)) \, g'(x) \). This means you differentiate the outer function \( f \) with respect to \( g \) and multiply by the derivative of the inner function \( g \) with respect to \( x \). This chaining allows us to peel back layers of complexity in functions, seamlessly managing nested relationships.
Trigonometric Functions
Trigonometric functions like sine and cosine are central to a vast array of problems in calculus. Differentiating these functions requires recognition of some key patterns:
- The derivative of \( \sin(x) \) is \( \cos(x) \).
- The derivative of \( \cos(x) \) is \( -\sin(x) \).
Differentiation Techniques
Differentiation techniques are the methods used to find the rate at which a function changes. In calculus, these techniques are crucial for understanding how to navigate more complex expressions:
- The Product Rule is applied when differentiating products of functions.
- The Chain Rule is employed for nested functions.
- Special rules exist for trigonometric functions.