Chapter 3: Problem 8
Find \(d y / d x\). $$g(x)=\frac{\cos x}{\sin ^{2} x}$$
Short Answer
Expert verified
The derivative is \( g'(x) = -\frac{1\text{sin}^2 x + 2\text{cos}^2 x }{\text{sin}^3 x} \).
Step by step solution
01
Rewrite the function
Rewrite the given function in a simpler form to make differentiation easier: \[ g(x) = rac{ ext{cos } x}{( ext{sin } x)^2} = ext{cos } x imes ( ext{sin } x)^{-2} \] This simplification helps us apply the product rule more effectively.
02
Apply the Product Rule
The product rule states: if \( u(x) \) and \( v(x) \) are functions of \( x \), then the derivative of their product is: \[ \frac{d}{dx}[u imes v] = u' v + u v' \] Here, let \( u(x) = \text{cos } x \) and \( v(x) = ( ext{sin } x)^{-2} \). Differentiate each function individually.
03
Differentiate \( u(x) = \cos x \)
Find the derivative of \( u(x) = \cos x \):\[ u'(x) = -\sin x \]
04
Differentiate \( v(x) = ( ext{sin } x)^{-2} \) using the chain rule
Apply the chain rule to differentiate \( v(x) = ( ext{sin } x)^{-2} \). The derivative is:\[ v'(x) = -2( ext{sin } x)^{-3} \cdot \cos x \] (Differentiate the power using the chain rule: \( n f(x)^{n-1} f'(x) \)).
05
Combine results using the Product Rule
Substitute \( u'(x) \), \( v(x) \), \( u(x) \), and \( v'(x) \) into the product rule formula:\[ g'(x) = (-\sin x) imes ( ext{sin } x)^{-2} + \cos x \times (-2( ext{sin } x)^{-3} \cdot \cos x) \] This simplifies to: \[ g'(x) = -\frac{1}{\text{sin } x} - \frac{2 \text{cos }^2 x}{\text{sin }^3 x} \]
06
Simplify the expression for the derivative
Combine the terms over a common denominator:\[ g'(x) = -\frac{1\text{sin}^2 x + 2\text{cos}^2 x }{\text{sin}^3 x} \]Simplify further if possible by recognizing trigonometric identities or simplification.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Product Rule in Differentiation
In calculus, the product rule is a vital tool for differentiating functions that are products of two or more functions. When you have a function like \( g(x) = u(x) \cdot v(x) \), you can find its derivative using the product rule:
- First, identify the two parts, \( u(x) \) and \( v(x) \).
- Calculate the individual derivatives, \( u'(x) \) and \( v'(x) \).
- Then, use the formula: \( \frac{d}{dx}[u \cdot v] = u' v + u v' \).
Chain Rule Explained
The chain rule is another fundamental method in calculus that allows you to differentiate composite functions. If you have a function \( h(x) = f(g(x)) \), the chain rule helps you by separating the tasks:
- First, differentiate the outer function \( f \) concerning its input, \( g(x) \).
- Then, multiply this result by the derivative of the inner function \( g(x) \).
Understanding Trigonometric Functions in Differentiation
Trigonometric functions such as \( \sin x \) and \( \cos x \) are ubiquitous in mathematical problems and often appear in differentiation exercises. They follow specific rules:
- The derivative of \( \sin x \) is \( \cos x \).
- The derivative of \( \cos x \) is \(-\sin x \).