Answer
$\frac{(x - 7)(x - 6)}{(x + 7)(x + 2)}$
Work Step by Step
$\frac{x^2 - 13x + 42}{x^2 + 10x + 21}$ $\div$ $\frac{x^2 - 4}{x^2 + x - 6}$
= $\frac{(x - 7)(x - 6)}{(x + 7)(x + 3)}$ $\div$ $\frac{(x + 2)(x - 2)}{(x + 3)(x - 2)}$
= $\frac{(x - 7)(x - 6)}{(x + 7)(x + 3)}$ $\times$ $\frac{(x + 3)(x - 2)}{(x + 2)(x - 2)}$
= $\frac{(x - 7)(x - 6)}{(x + 7)(x + 3)}$ $\times$ $\frac{(x + 3)}{(x + 2)}$
= $\frac{(x - 7)(x - 6)}{(x + 7)(x + 2)}$
