So du is equal to seven times dx. That part right over there is equal to du. And if we want to care about u, well, that's just going to be the seven x plus nine. That is our u. So let's rewrite this indefinite integral in terms of u. It's going to be equal to 1 7th times the integral of, and I'll just take the seven and put it in the back so we can just write the square root of u, square root of u, du, seven times dx is du. And we can rewrite this if we want as u to the 1 1⁄2 power.