Algebra: A Combined Approach (4th Edition)

$\dfrac{5x^{2}-125}{x^{2}+2x-15}=\dfrac{5(x-5)}{x-3}$
$\dfrac{5x^{2}-125}{x^{2}+2x-15}$ Take out common factor $5$ from the numerator and factor the denominator: $\dfrac{5x^{2}-125}{x^{2}+2x-15}=\dfrac{5(x^{2}-25)}{(x+5)(x-3)}=...$ Factor $x^{2}-25$ and simplify: $...=\dfrac{5(x-5)(x+5)}{(x+5)(x-3)}=\dfrac{5(x-5)}{x-3}$