# Integrate. {eq}\int \sin \theta \sin 3 \theta d \theta{/eq}

## Question:

Integrate.

{eq}\int \sin \theta \sin 3 \theta d \theta{/eq}

## Integration of Trigonometric Functions:

The indefinite integral can be expressed without boundaries and contains an arbitrary constant {eq}C {/eq}. The method of u-substitution is also known as the reverse-chain rule. This method entails the substitution of the integrand, such that the entire argument of the integral is transformed. The integration process proceeds with the transformed variable but the final answer is expressed in terms of the original variables. A function in terms of trigonometric can be evaluated using trigonometric identities.