ispymalik

i had a question on how substitution works exactly. i know that the dervitive of the sub. needs to be infront. but what if its not? lets take an example. x^2 sqrt(x^3 +1) here you would make x^3 + 1 = u and du would be 3x^2 but you have only x^2 infront would'nt dividing by 3 change it? what if for example you only had x infront? maybe im just confused *sighs*