This trick for evaluating integrals utilizes the fact that any [[probability density function]] integrated over the [[support]] of the distribution equals $1$. If you have a difficult integral, and you can make it resemble a distribution whose pdf you know, multiply the integral by constants that allow you to transform the integral to the pdf you know, pull the constants outside of the integral, and then drop the integral. #expand (see 5002 week 1 lesson 8)