What is the derivative of ln(sin(x))?

Understand the Problem

The question is asking for the derivative of the natural logarithm of the sine function, ln(sin(x)). To solve this, we will apply the chain rule of differentiation.

Answer

The derivative of $\ln(\sin(x))$ is $y' = \cot(x)$.
Answer for screen readers

The derivative of $\ln(\sin(x))$ is $y' = \cot(x)$.

Steps to Solve

  1. Identify the function to differentiate

We need to differentiate the function $y = \ln(\sin(x))$.

  1. Apply the chain rule

To differentiate this, we use the chain rule, which states that if you have a composite function $y = f(g(x))$, then the derivative $y'$ is given by

$$ y' = f'(g(x)) \cdot g'(x) $$

Here, $f(g) = \ln(g)$ where $g(x) = \sin(x)$.

  1. Differentiate the outer function

First, we differentiate the outer function $f(g) = \ln(g)$.

The derivative of $\ln(g)$ is

$$ f'(g) = \frac{1}{g} $$

  1. Differentiate the inner function

Next, we differentiate the inner function $g(x) = \sin(x)$.

The derivative of $\sin(x)$ is

$$ g'(x) = \cos(x) $$

  1. Combine the derivatives

Now we combine the results from steps 3 and 4 using the chain rule:

$$ y' = f'(g) \cdot g'(x) $$

Substituting $g = \sin(x)$:

$$ y' = \frac{1}{\sin(x)} \cdot \cos(x) $$

This simplifies to:

$$ y' = \frac{\cos(x)}{\sin(x)} $$

  1. Final simplification

We recognize that $\frac{\cos(x)}{\sin(x)}$ can be simplified further to:

$$ y' = \cot(x) $$

The derivative of $\ln(\sin(x))$ is $y' = \cot(x)$.

More Information

The derivative of the natural logarithm of the sine function is important in calculus as it appears frequently in problems involving trigonometric functions and logarithmic identities. The cotangent function, $\cot(x)$, is simply the reciprocal of the tangent function, providing insights into relationships in trigonometry.

Tips

  • Forgetting to apply the chain rule correctly, which can lead to incorrect derivatives.
  • Misremembering the derivatives of trigonometric functions, like confusing $\sin(x)$ with $\cos(x)$.

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