I'm trying to reduce the following expression. The steps follow an online CAS and I have a question regarding a step.
$= (b-1)(\frac {1-b^n} {1-b})$
$= \frac {(1-b^n)(b-1)} {1-b}$
The next steps indicates cancellation. Does anyone know what is being canceled?
$= -(-b^n + 1) = b^n - 1$
I have put the cancelled parts in boldface so you can see them.
$$(b-1)\left(\frac {1-b^n} {1-b}\right) =\frac{(b-1)(1-b^n)}{1-b} =\frac{\mathbf{(b-1)}(1-b^n)}{-\mathbf{(b-1)}}=\frac{(1-b^n)}{-1}=(b^n-1)$$