Chapter 3: Problem 22
Find \(d s / d t\) $$ s=\frac{\sin t}{1-\cos t} $$
Short Answer
Expert verified
The derivative \( \frac{ds}{dt} \) is \( -\frac{1}{1 - \cos t} \).
Step by step solution
01
Identify the quotient rule
We are given a function \( s = \frac{\sin t}{1 - \cos t} \).\ To differentiate a quotient, we'll use the quotient rule: if \( u(t) = \sin t \) and \( v(t) = 1 - \cos t \), then the derivative \( \frac{ds}{dt} \) is given by:\[ \frac{d}{dt}\left( \frac{u}{v} \right) = \frac{v \cdot \frac{du}{dt} - u \cdot \frac{dv}{dt}}{v^2} \].
02
Differentiate the numerator
Differentiate the numerator \( u(t) = \sin t \). The derivative \( \frac{du}{dt} \) is \( \cos t \).
03
Differentiate the denominator
Differentiate the denominator \( v(t) = 1 - \cos t \). The derivative \( \frac{dv}{dt} \) is \( \sin t \) since the derivative of \(-\cos t\) is \( \sin t \).
04
Apply the quotient rule
Substitute the derivatives and the functions back into the quotient rule formula: \[ \frac{ds}{dt} = \frac{(1 - \cos t) \cdot \cos t - \sin t \cdot \sin t}{(1 - \cos t)^2} \].
05
Simplify the expression
Simplify the expression for \( \frac{ds}{dt} \): \[ \frac{ds}{dt} = \frac{\cos t - \cos^2 t - \sin^2 t}{(1 - \cos t)^2} \].\ Use the identity \( \cos^2 t + \sin^2 t = 1 \) to simplify further: \[ \cos^2 t + \sin^2 t = 1 \implies \sin^2 t = 1 - \cos^2 t \].\ Therefore, \( \cos^2 t + \sin^2 t = 1 \) can help in rewriting the expression as \[ \frac{ds}{dt} = \frac{\cos t - 1}{(1 - \cos t)^2} = \frac{-(1 - \cos t)}{(1 - \cos t)^2} \].\ Finally, simplify to: \[ \frac{ds}{dt} = -\frac{1}{(1 - \cos t)} \].
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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 crucial concept in calculus for finding the derivative of a function that is the ratio of two differentiable functions. If you have a function that can be expressed as a fraction, such as \( s = \frac{u(x)}{v(x)} \), you need the quotient rule to differentiate it. Here's the formula that the quotient rule uses:
- \( \frac{d}{dt}\left( \frac{u}{v} \right) = \frac{v \cdot \frac{du}{dt} - u \cdot \frac{dv}{dt}}{v^2} \)
Trigonometry
Trigonometry plays a fundamental role when dealing with derivatives of functions involving sine and cosine. Here, we're working with \( \sin t \) and \( 1 - \cos t \). Understanding the derivatives of these basic trigonometric functions is vital:
- The derivative of \( \sin t \) is \( \cos t \).
- The derivative of \( 1 - \cos t \) requires applying the derivative of \( -\cos t \), which is \( \sin t \).
Derivative Simplification
Simplifying the derivative expression is the final step and often involves using trigonometric identities. After applying the quotient rule, we obtained:
- \( \frac{ds}{dt} = \frac{(1 - \cos t) \cdot \cos t - \sin t \cdot \sin t}{(1 - \cos t)^2} \)
- Substitute \( \sin^2 t = 1 - \cos^2 t \) from the identity \( \cos^2 t + \sin^2 t = 1 \).
- This substitution helps in revising \( \cos t - \cos^2 t - \sin^2 t \) to \( \cos t - 1 \).
- The numerator simplifies to \( -(1 - \cos t) \).
- Mastering simplification ensures error-free and efficient calculus solutions, and aids in better understanding of function behavior.