My book has an example that I am having trouble comprehending
"Subsititution 1: The composite function suggests the new variable u = x+1. You might doubt whether this choice will work becuase du=dx and the x in the numerator of the integrand is unnacounted for. But, lets proceed. Letting u = x+1, we have x=u-1, du=dx, and"
How should I know to let x= u-1