Is there any formula I'm unaware of?

Question

$\int_{ac}^{ab} {f(x)}dx = \int_{c}^{b } {f(ax)}dx$

Is there any definite integral formula like this? I was studying improper integrals and suddenly I found an application of that formula (though I'm not sure). I've searched through the web but nothing I found related to this.

This is what I found on my textbook

Answer 1

The formula should be

$$\int_{ac}^{ab}f(x)dx=a\int_c^bf(ax)dx$$