# Integration by substitution .

## Main Question or Discussion Point

Integration by substitution.....

Accroding to my notes, when performing integration by substitution, du/dx= f'(x), and therefore du = f'(x)*dx. But how is this possible? We are treatnig dy/dx as if it were a fraction - but in essence it is not! So why is this statement still true?

Thanks.

Hurkyl
Staff Emeritus