When do you use u-substitution in integration?

U-substitution in integration is used when you have an integral that is a product of functions, where one function is the derivative of the other (up to a constant factor). Here are the steps to use u-substitution:

1. Identify a part of the integrand that appears to be the derivative of another part. This part will be your "u".

2. Substitute the identified part with "u". The derivative of this part will be "du".

3. Rewrite the integral in terms of "u".

4. Perform the integration with respect to "u".

5. Substitute "u" back in terms of the original variable to get the final answer.

Remember, u-substitution is essentially the reverse of the chain rule from differentiation. It's a method to simplify the integral, making it easier to solve.