Question

ДАЮ 37 БАЛЛОВ,ПОМОГИТЕ
$frac{5ab}{a+5b} *( frac{a}{5b}- frac{5b}{a})$
a=5√7+9
b=√7-9

Answer 1

$frac{5ab}{a+5b} * frac{a^2-(5b)^2}{5ab} =frac{5ab}{a+5b}* frac{(a-5b)(a+5b)}{5ab}= frac{a-5b}{1}=5 sqrt{7} +9-5 sqrt{7} + 5*9= \ 54$