Question

решите пжжжжж срочно!!!!!!!!!!!!!!Даю 30 балов!!!!!

Answer 1

№1

$\frac{1}{b} = \frac{1}{c} - \frac{1}{a}\\\frac{1}{b} = \frac{a-c}{ac}\\b = \frac{ac}{a-c}$

Ответ: 2 (ac/(a-c)).

№2

$\frac{(x-7)(x+7)}{3(x+7)} + \frac{7}{3} = \frac{x-7}{3} + \frac{7}{3} = \frac{x}{3}$.

Ответ: 2 (x/3).

№3

$\left \{ {{a-b=10} \atop {a^2-b^2=240}} \right. \\a = 10 + b\\(10+b)^2 - b^2 = 240\\100 + 20b + b^2 - b^2 = 240\\20b = 140\\b = 7\\a = 10 + b = 10 + 7 = 17$

Ответ: 4 (7 и 17).