Question

найдите значение выражения...​

Answer 1

$( frac{a + 3b}{ {a}^{2} - 3ab } - frac{1}{a} ) div frac{b}{3b - a} = \ = (frac{a + 3b}{a(a - 3b)} - frac{1}{a} ) times frac{3b - a}{b} = \ = frac{a + 3b - (a - 3b)}{a(a - 3b)} times frac{ - (a - 3b)}{b} = \ = frac{6b}{a} times frac{ - 1}{b} = - frac{6}{a}$
При а=7,5 получаем:
$- frac{6}{a} = - frac{6}{7.5} = - frac{60}{75} = \ = - frac{4}{5} = - 0.8$