Система уравнений: 5х + 3ху = -4 у - 3ху = -7

{ 5х + 3ху = -4        
{ у - 3ху = -7

{ y = -7/(1-3x)
{ 5x - 21x/(1-3x) = -4

5x(1 - 3x) - 21x = 12x - 4
5x - 15x² - 33x + 4 = 0
15x² + 28x - 4 = 0          D = b²-4ac = 784+240 = 1024 = 32²

x₁ = (-b+√D)/2a = 2/15         y₁ = -7/(1-0,4) = -11 2/3
x₂ = (-b -√D)/2a = -2              y₂ = -7/(1+6) = -1

ответ: {2/15; -11 2/3}, {-2; -1}