Chapter 3: Problem 62
In Exercises \(51-70,\) find \(d y / d t\). $$y=\cos \left(5 \sin \left(\frac{t}{3}\right)\right)$$
Short Answer
Expert verified
\( \frac{dy}{dt} = -\frac{5}{3} \cdot \sin(5 \sin(\frac{t}{3})) \cdot \cos(\frac{t}{3}) \)."}
Step by step solution
01
Understand the Function Composition
The given function is a composition of multiple functions. First, there's a sine function applied to \(\frac{t}{3}\), then that result is passed into another sine function, and finally, the cosine function is applied. Thus, we have three layers of functions: \(y = \cos(u)\), where \(u = 5 \cdot \sin(v)\), and \(v = \frac{t}{3}\).
02
Differentiate the Outer Function
Differentiate the outermost function using the chain rule. The derivative of \(y = \cos(u)\) with respect to \(u\) is \(-\sin(u)\). So, \( \frac{dy}{du} = -\sin(u)\).
03
Differentiate the Middle Function
Now differentiate the middle function \(u = 5 \cdot \sin(v)\) with respect to \(v\). The derivative is \( \frac{du}{dv} = 5 \cdot \cos(v)\).
04
Differentiate the Innermost Function
Differentiate the innermost function \(v = \frac{t}{3}\) with respect to \(t\). The derivative is \( \frac{dv}{dt} = \frac{1}{3}\).
05
Apply the Chain Rule
To find \( \frac{dy}{dt}\), we apply the chain rule to combine all these derivatives: \( \frac{dy}{dt} = \frac{dy}{du} \cdot \frac{du}{dv} \cdot \frac{dv}{dt} = -\sin(u) \cdot 5 \cdot \cos(v) \cdot \frac{1}{3} \).
06
Substitute the Expressions Back
Substitute \(u = 5 \sin(v)\) and \(v = \frac{t}{3}\) back into the expression: \( \frac{dy}{dt} = -\sin(5 \sin(\frac{t}{3})) \cdot 5 \cdot \cos(\frac{t}{3}) \cdot \frac{1}{3}\).
07
Simplify the Expression
Simplify \( \frac{dy}{dt}\): \( \frac{dy}{dt} = -\frac{5}{3} \cdot \sin(5 \sin(\frac{t}{3})) \cdot \cos(\frac{t}{3}) \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Composition of Functions
When dealing with the composition of functions, you're essentially working with a function inside another function. This can be thought of like layers of an onion. In the given exercise, we have three layers: the outer cosine function, an inner sine function, and the innermost being a simple linear expression \( t/3 \).
- The innermost function, \( v = \frac{t}{3} \), is evaluated first, transforming \( t \).
- The result, \( v \), is then plugged into the trigonometric function \( u = 5 \cdot \sin(v) \), creating another layer.
- Finally, this result, \( u \), enters the final layer with the function \( y = \cos(u) \).
Trigonometric Differentiation
Trigonometric differentiation deals with finding the derivatives of trigonometric functions, which are common in calculus problems. In this exercise, both the sine and cosine functions are involved.
**How to Differentiate Sine and Cosine:**
**How to Differentiate Sine and Cosine:**
- The derivative of \( \sin(x) \) with respect to \( x \) is \( \cos(x) \).
- The derivative of \( \cos(x) \) with respect to \( x \) is \( -\sin(x) \).
- We first differentiate the cosine function, resulting in \( -\sin(u) \).
- Then, the sine function inside needs differentiation, giving \( 5 \cdot \cos(v) \) where \( v = \frac{t}{3} \).
Calculus Problem Solving
Solving calculus problems often involves recognizing patterns and functions within functions to properly apply differentiation rules. Let's break down this common calculus approach:
**Step-by-Step Application:**
**Step-by-Step Application:**
- Identify all the functions within the problem statement.
- Differentiate from the outermost to the innermost function systematically using the chain rule.
- We start with the differentiation of the outer cosine layer, using the chain rule to manage each subsequent layer.
- The process involves multiplying derivatives step by step: from the outermost, \( -\sin(u) \), to middle \( 5 \cdot \cos(v) \), and the inner \( \frac{1}{3} \).
- Finally, substitute back to ensure your expression represents the rate of change correctly.