1. ## simplifying

i am very confused on this, how do you get 36(x^2 -1)/(x^2 + 3)^3 from simplifying the top?

i divided the numerator and denominators and got -12 + 48x^2 /(x^2+3) which is different from the answer; can someone please explain it clearly

2. If you divide the top and the bottom by $*x^2 +3$*then you get
$\frac{-12(x^2+3)+48x^2}{(x^2 +3)^3} \frac{-12x^2-36)+48x^2}{(x^2 +3)^3} = \frac{36(x^2-1)}{(x^2 +3)^3}$