# calculus – How to make a substitution in U with this result?

I saw this on a website. I work on Integrals and U-substitution does not make sense.

The initial problem was $$int$$x / x + 1$$dx$$

The U-Sub did u = x + 1, du = dx

so he gave me a $$int$$u-1 / u of the …

How did my question become the numerator?