Решите карточку по алгебре,состоящую из 4 заданий

1) с(3х+5у)- у (5с- 2х)= =3сх+5ус-5ус+2ху=
=3сх+2ху

2)
$\frac{15 b}{5 - b} -3 b = \frac{15b - 15b + 3 {b}^{2} }{5 - b} = \frac{3 {b}^{2} }{5 - b}$
3) 4х-4х²=1
4х²-4х+1=0
(2х-1)²=0
2х-1=0
х=½

4)
$\frac{4}{ {x}^{2} - 9 } - \frac{2}{ {x}^{2} + 3x } = \\ = \frac{4}{(x - 3)(x + 3)} - \frac{2}{x(x + 3)} = \\ = \frac{4x - 2(x - 3)}{x(x - 3)(x + 3)} = \frac{2x + 6}{x(x - 3)(x + 3)} = \\ = \frac{2(x + 3)}{x(x - 3)(x + 3)} = \frac{2}{x(x - 3)}$
(при х≠±3, х≠0)