Chapter 3: Problem 10
Find the derivatives of the functions. Assume \(a, b,\) and \(c\) are constants. $$g(\theta)=\sin ^{2}(2 \theta)-\pi \theta$$
Short Answer
Expert verified
The derivative of the function is \( g'(\theta) = 2\sin(4\theta) - \pi \).
Step by step solution
01
Apply the Chain Rule to the First Term
The function can be written as \( g(\theta) = (\sin(2\theta))^2 - \pi\theta \). The first part requires the chain rule, which states \( \frac{d}{dx}[f(g(x))] = f'(g(x))g'(x) \). Here, let \( u = \sin(2\theta) \), so \( g(\theta) = u^2 \). The derivative of \( u^2 \) with respect to \( u \) is \( 2u \), and the derivative of \( u = \sin(2\theta) \) using the chain rule involves the derivative \( \frac{d}{d\theta}[\sin(2\theta)] = 2\cos(2\theta) \).
02
Apply Derivative of Sine Squared
Using the results from Step 1, calculate the derivative of the first part: \[ \frac{d}{d\theta}[\sin^2(2\theta)] = 2\sin(2\theta) \cdot \frac{d}{d\theta}[\sin(2\theta)] = 2\sin(2\theta) \cdot 2\cos(2\theta). \] Simplify it to: \[ 4\sin(2\theta)\cos(2\theta). \]
03
Apply the Double Angle Formula
Recognize that the expression \( 4\sin(2\theta)\cos(2\theta) \) can be simplified using the double angle identity \( \sin(2A) = 2\sin(A)\cos(A) \). Thus, \( 4\sin(2\theta)\cos(2\theta) = 2\sin(4\theta) \).
04
Derivative of the Linear Term
The second part of the function is \( -\pi\theta \). The derivative of \( -\pi\theta \) with respect to \( \theta \) is simply \( -\pi \) because \( \pi \) is a constant.
05
Combine the Results
Combine the derivatives from Step 3 and Step 4 to get the derivative of the entire function: \[ g'(\theta) = 2\sin(4\theta) - \pi. \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivative
The derivative is a core concept of calculus that measures how a function changes as its input changes. Simply put, it describes the rate at which something is changing. Imagine driving a car: your speed at any moment is the "derivative" of your position with respect to time. In this exercise, our task was to find the derivative of the function \( g(\theta) = \sin^2(2\theta) - \pi\theta \). Essentially, we needed to determine how this function changes as \( \theta \) varies. When finding a derivative, follow these steps:
- Identify each term that needs differentiation.
- Use rules like the chain rule or product rule, when necessary.
- Simplify your result to get the simplest form of the derivative.
Chain Rule
The chain rule is a powerful tool in calculus for finding derivatives of composite functions. A composite function is a function composed of two or more functions, such as \( f(g(x)) \). The chain rule allows us to differentiate such functions piece by piece. It states: if \( y = f(u) \) and \( u = g(x) \), then \( \frac{dy}{dx} = \frac{dy}{du} \cdot \frac{du}{dx} \).In our original exercise, we used the chain rule to differentiate \( (\sin(2\theta))^2 \). Here's how it was applied:
- Let \( u = \sin(2\theta) \).
- The outer function becomes \( u^2 \), whose derivative is \( 2u \).
- The inner function is \( u = \sin(2\theta) \), with derivative \( 2\cos(2\theta) \).
Trigonometric Functions
Trigonometric functions, like sine and cosine, are foundational in calculus due to their periodic nature and relationships. They describe the ratios of a right triangle's sides in relation to its angles and have applications in various fields like physics, engineering, and beyond.In our exercise, the function \( \sin^2(2\theta) \) incorporates the sine function, which varies between -1 and 1. Understanding how to differentiate trigonometric functions is essential.
- The derivative of \( \sin(x) \) is \( \cos(x) \).
- The derivative of \( \cos(x) \) is \( -\sin(x) \).
- For \( \sin^2(x) \), you use the chain rule to differentiate.
Double Angle Formula
The double angle formula is a trigonometric identity that simplifies expressions involving trigonometric functions of double angles. The formula for sine, which is particularly helpful, is \( \sin(2A) = 2\sin(A)\cos(A) \).In our solution, we recognized the expression \( 4\sin(2\theta)\cos(2\theta) \) and employed the double angle formula to simplify it to \( 2\sin(4\theta) \). Here's why the double angle formula is useful:
- It can transform products of trigonometric functions into simpler expressions.
- It is essential for solving integrals involving trigonometric identities.
- It enables simplification of many trigonometric identities and equations.