Question

решите:
$frac{b}{a-b} ( frac{1}{a} - frac{1}{b})$

Answer 1

 = $frac{b}{a-b}* frac{b-a}{ab}= frac{b-a}{a(a-b)}= - frac{a-b}{a(a-b)}= - frac{1}{a}$