Question

Выражение (36a^2\ 5a2+13a-6 - 5a-2\a+3 ) : 11a-2 \ a^2-2a-15 - 28a-a^2\2-5a

Answer 1

$( \frac{36 {a}^{2} }{5 {a}^{2} + 13a - 6 } - \frac{5a - 2}{a + 3} ) \div \frac{11a - 2}{ {a}^{2} - 2a - 15 } - \frac{28a - {a}^{2} }{2 - 5a}$
Разложим 5a^2 + 13a - 6 на множители.
$d = {b}^{2} - 4ac = 169 - 4 \times 5 \times ( - 6) = 169 + 120 = 289 \\ x1 = \frac{ - 13 + 17}{2 \times 5} = \frac{4}{10} = \frac{2}{5} \\ x2 = \frac{ - 13 - 17}{2 \times 5} = \frac{ - 30}{10} = - 3 \\ 5 {x}^{2} + 13a - 6 = 5(a - \frac{2}{5} )(a + 3) = (5a - 2)(a + 3)$
Разложим a^2 - 2a - 15 на множители:
$d = {b}^{2} - 4ac = 4 - 4 \times ( - 15) = 64 \\ a1 = \frac{2 + 8}{2} = 5 \\ a2 = \frac{2 - 8}{2} = - 3 \\ {a}^{2} - 2a - 15 = (a - 5)(a + 3)$
$( \frac{36 {a}^{2} }{(5a - 2)(a + 3)} - \frac{5a - 2}{a + 3} ) \div \frac{11a - 2}{(a - 5)(a + 3)} - \frac{28 a - {a}^{2} }{2 - 5a} = \frac{36 {a}^{2} - {(5a - 2)}^{2} }{(5a - 2)(a + 3)} \div \frac{11a - 2}{(a - 5)(a + 3)} - \frac{28a - {a}^{2} }{ - (5a - 2)} = \frac{(6a + 5a - 2)(6a - 5a + 2)}{(5a - 2)(a + 3)} \times \frac{(a - 5)(a + 3)}{11a - 2} + \frac{28a - {a}^{2} }{5a - 2} = \frac{(11a - 2)(a + 2)}{5a - 2} \times \frac{a - 5}{11a - 2} + \frac{28a - {a}^{2} }{5a - 2} = \frac{(a + 2)(a - 5)}{5a - 2} + \frac{28a - {a}^{2} }{5a - 2} = \frac{ {a}^{2} + 2a - 5a - 10 + 28a - {a}^{2} }{5a - 2} = \frac{25a - 10}{5a - 2} = \frac{5(5a - 2)}{5a - 2} = 5$