Hello all, We've just begun integration in my maths class and I have a question about a certain aspect of integration by substitution. Let's say for instance you let u = 2x-1. Then you differentiate it and get du/dx = 2. My maths teacher said " you can now think of it as multiplying across by 'dx' ". Which leads to du = 2dx. My question is, what mathematical operations are you actually committing to achieve this line? Thanks in advance for any help.