You are Here: Home >< Maths

# Integration by Substitution watch

1. When using u substitution to evaluate an integral why is it possible to treat du/dx as a fraction and rearrange to replace dx?
2. you aren't treating it as a fraction any more than you do when you solve a differential equation, you are just changing the variable you are integrating with respect to. if you want a proper answer, you'll have to ask someone good i.e. nuodai
3. There are a few answers I can give to this question depending on the level you're working out. If you're doing A-level, the answer is "you just can". If you're doing anything higher, the answer really is that you can't except for notation's sake. So when we write we do so on the understanding that we're going to do something else with the equation, for example integrate both sides to give something like , or "divide through" by a differential to give something like or . This is possible because rules like the chain rule make it possible.
4. (Original post by nuodai)
There are a few answers I can give to this question depending on the level you're working out. If you're doing A-level, the answer is "you just can". If you're doing anything higher, the answer really is that you can't except for notation's sake. So when we write we do so on the understanding that we're going to do something else with the equation, for example integrate both sides to give something like , or "divide through" by a differential to give something like or . This is possible because rules like the chain rule make it possible.
thank you

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: September 27, 2010
Today on TSR

### He lied about his age

Thought he was 19... really he's 14

### University open days

Wed, 25 Jul '18
2. University of Buckingham
Wed, 25 Jul '18
3. Bournemouth University
Wed, 1 Aug '18
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams