Question

Помогите номер 3 и 10 пожалуйста.

Answer 1

3)

$\frac{x}{y} + \frac{y}{x} = \frac{ {x}^{2} + {y}^{2} }{xy } = \frac{81}{45} = \frac{9}{5}$

10)

$\frac{a}{a + 4} - \frac{a}{a - 4} = \frac{ {a}^{2} - 4a - {a}^{2} - 4a}{ {a}^{2} - 16 } = - \frac{8a}{ {a}^{2} - 16} = - \frac{8 \times 6}{ {6}^{2} - 16 } = - \frac{12}{5}$