а) Чx + 18 = 2
4x = 2 - 18
4x = - 16
x = -16 / 4
x = - 4
b) 2x + 9 = -18 -x
2x + x = - 18 - 9
3x = - 27
x = - 27 / 3
x = - 9
c)[2x + y = 4
[3x - y = 4
[tex]2x + y = 4\\2x = 4 - y\\x = \frac{4 - y}{2}[/tex]
[tex]3x - y = 4\\3x = 4 + y\\x = \frac{4 + y}{3}[/tex]
[tex]\frac{4 - y}{2} = \frac{4 + y}{3} \\3 (4 - y) = 2 (4 + y)\\12 - 3y = 8 + 2y\\- 3y - 2y = 8 - 12\\-5y = - 4\\5y = 4\\y = 4 / 5[/tex]
[tex]x = \frac{4 - 4/5}{2}\\x = \frac{16/5}{2}\\x = 8/5[/tex]
