Question

Найдите значение выражения

Answer 1

$\frac{ac {}^{2} }{a {}^{2} - c {}^{2} } \times \frac{a - c}{ac} = \frac{c}{(a - c)(a + c)} \times \frac{(a - c)}{1} = \frac{c}{a + c} = \frac{9}{11 + 9} = \frac{9}{20}$