Решить систему уравнений. 2(x+y)^2-7(x+y)+3=0, 2x-3y=-1.

Ответ
{ 2(x+y)^2 - 7(x+y) + 3 = 0
{ 2x - 3y = -1

2(x+y)^2 - 7(x+y) + 3 = 0
x+y = t
2t^2 - 7t + 3 = 0
t1 = 3 => x+y = 3
t1 = 1/2 => x+y = 1/2

Решай 2 новые системы:
1) { x+y = 3 => y = 3-x
{ 2x - 3y = -1 => 2x-3*(3-x)=-1 => 4x=5 => x=5/4 => y=3-5/4=7/4

2) { x+y = 1/2 => y = 1/2-x
{ 2x - 3y = -1 => 2x-3*(1/2-x)=-1 => 10x=1 => x=1/10 => y=3-1/10=29/10