# Cancelling the signs

1. Jan 22, 2014

1. The problem statement, all variables and given/known data
This is the simplest problem you would ever get.
$\frac{-fu}{s-f}=\frac{fu}{-s+f}$
This is true.
So the signs can be cancelled.What are the rules for doing that?
I guess I was not listening to the teacher when I first learned algebra.

3. The attempt at a solution
Don't think that I don't know algebra.I just want to know the rules of THAT.

2. Jan 22, 2014

### Tanya Sharma

Multiplying numerator and denominator of a rational number by a non zero number keeps it unchanged .The non zero number in this case is -1.

3. Jan 22, 2014