Description
When you use substitution in definite integrals, you have two options for dealing with the limits of integration. When you make the substitution, change the limits of integration so that they're associated with the substitution variable, instead of with the original variable. If you do this, you'll be able to plug the new limits of integration directly into the integrated function. When you make the substitution, leave the limits of integration in terms of the original variable. If you do this, you'll have to back-substitute to get the integration in terms of the original variable before evaluating over the limits of integration.