Question

Найдите значение выражения 4а/а^2-36 - 2/а-6 при а=-10

Answer 1

$\frac{4a}{a^2-36} - \frac{2}{a-6} = \frac{4a}{(a-6)(a+6)} -\frac{2}{a-6}= \frac{4-2(a+6)}{(a-6)(a+6)} = \frac{4a-2a-12}{(a-6)(a+6)} = \frac{2a-12}{(a-6)(a+6)} \\ \\ = \frac{2(a-6)}{(a-6)(a+6)} = \frac{2}{a+6} \\ \\ \\ \frac{2}{-10+6}= \frac{2}{-4} = \frac{1}{-2} =- \frac{1}{2} =-0,5$