Даю 40б!!! Решение письменно

Задание 5.

$a) \frac{9 {x}^{10} {(3x)}^{ - 2} }{ {( {x}^{ - 3} )}^{ - 2} } = \frac{9 {x}^{10} }{ {x}^{6} \times 9 {x}^{2} } = {x}^{2}$

$b) \frac{12 {b}^{ - 4} }{ {a}^{ - 4} } \times \frac{ {a}^{3} }{4 {b}^{3} } = 3 {b}^{ - 7} {a}^{ 7} = 3 \frac{ {a}^{7} }{ {b}^{7} }$

Задание 3.

$( \frac{a + 1}{a - 1} - \frac{4a}{ {a}^{2} - 1} ) \div \frac{a - 1}{ {a}^{2} + a} = \\ = \frac{(a + 1) \times (a + 1) - 4 a}{ (a - 1)(a + 1)} \times \frac{ a(a + 1)}{ a - 1} = \\ = \frac{ {a}^{2} + 2a + 1- 4 a}{a - 1} \times \frac{ a}{ a - 1} = \\ = \frac{{a}^{2} - 2a + 1}{ a - 1} \times \frac{ a}{ a - 1} = \\ = \frac{ a{(a - 1)}^{2} }{{(a - 1)}^{2}} = a$