Question

Найдите значение выражения 21/(3a-a^2)-7/a при a =-32

Answer 1

$\frac{21}{3a-a^2} - \frac{7}{a} = \frac{21}{a(3-a)} - \frac{7}{a} = \frac{21-7\cdot (3-a)}{a(3-a)} =\frac{21-21+7a}{a(3-a)}= \frac{7a}{a(3-a)} = \frac{7}{3-a} = \\=\frac{7}{3+32}= \frac{7}{35} = \frac{1}{5}$