Chapter 2: Problem 54
Find the derivative of the function. $$ g(t)=\tan (\cos 2 t) $$
Short Answer
Expert verified
The derivative of the function \(g(t) = \tan(\cos 2t)\) is:
\[\frac{dg}{dt} = -2\sin(2t)\sec^2(\cos 2t)\]
Step by step solution
01
Identify the chain rule formula
The chain rule states that the derivative of a composite function is the derivative of the outer function times the derivative of the inner function. In other words, if we have a function \(y = f(g(x))\), then its derivative with respect to x is given by:
\[ \frac{dy}{dx} = \frac{df}{dg} \cdot \frac{dg}{dx} \]
02
Apply the chain rule
In our case, \(g(t) = \tan(\cos 2t)\). Let's rewrite it as a composition of two functions:
\[f(u) = \tan(u) \quad \text{and} \quad u = \cos 2t\]
Now we need to find the derivatives of both functions with respect to their respective variables:
1. Derivative of \(f(u)\) with respect to u:
\[ \frac{df}{du} = \frac{d}{du}\tan(u) \]
2. Derivative of \(u\) with respect to t:
\[ \frac{du}{dt} = \frac{d}{dt}(\cos 2t) \]
03
Find the derivatives of the individual functions
1. The derivative of \(f(u) = \tan(u)\) with respect to u is:
\[ \frac{df}{du} = \frac{d}{du}\tan(u) = \sec^2(u) \]
2. The derivative of \(u = \cos 2t\) with respect to t is:
\[\frac{du}{dt} = \frac{d}{dt}(\cos 2t) = -2\sin(2t)\]
04
Use chain rule to compute the derivative of the main function
Now using the chain rule to find the derivative of the main function \(g(t) = \tan(\cos 2t)\):
\[\frac{dg}{dt} = \frac{df}{du} \cdot \frac{du}{dt} = \sec^2(u) \cdot (-2\sin(2t))\]
Since \(u = \cos 2t\), substitute back in the expression:
\[\frac{dg}{dt} = \sec^2(\cos 2t) \cdot (-2\sin(2t))\]
So, the derivative of the function \(g(t) = \tan(\cos 2t)\) is:
\[\frac{dg}{dt} = -2\sin(2t)\sec^2(\cos 2t)\]
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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 powerful tool in calculus for finding the derivative of composite functions. When we have a function of a function, the chain rule helps us work out the overall derivative by focusing on each part. Consider a function like \( y = f(g(x)) \). The chain rule tells us to differentiate the outer function \( f \) and multiply it by the derivative of the inner function \( g \). The formula is:
- \( \frac{dy}{dx} = \frac{df}{dg} \cdot \frac{dg}{dx} \)
Composite Functions
Composite functions are like nesting functions inside one another. For example, in \( g(t) = \tan(\cos 2t) \), there are two distinct functions: \( \tan(u) \) as the outer function and \( \cos 2t \) as the inner function. You break it down as:
- \( f(u) = \tan(u) \)
- \( u = \cos 2t \)
Trigonometric Derivatives
Derivatives of trigonometric functions are a key part of calculus, helping analyze periodic patterns. Recognizing these derivatives can make solving problems much simpler:
- \( \frac{d}{du} \tan(u) = \sec^2(u) \)
- \( \frac{d}{dt} \cos(2t) = -2\sin(2t) \)