Question

Aratati ca $\frac{ x^{2} -2x - 15 }{ x^{2} + 10 x + 21 } = \frac{x-5}{x+7}$

Answer 1

$\frac{ x^{2} -2x-15}{ x^{2} +10x+21} = \frac{ x^{2} -5x+3x-15}{ x^{2} +3x+7x+21} = \frac{x(x-5)+3(x-5)}{x(x+3)+7(x+3)} = \frac{(x-5)(x+3)}{(x+3)(x+7)}= \frac{x-5}{x+7} .$