Question

How do you simplify `(4(x^2) - 36) / (x^2 + 10x + 21)` and what are the restrictions?

Answer 1

First you factorise, then you may cancel.

Explanation:

`=(4*(x^2-9))/((x+3)(x+7))=(4cancel((x+3))(x-3))/(cancel((x+3))(x+7))`

`=(4(x-3))/(x+7)`

Restrictions : `x!=-3andx!=-7`
as these would make the denominator of the original `=0`
`x=-3` is the worst, as this would create a `0/0` situation, a capital sin in maths.