Система уравнений:

5 х + 3 ху = - 4

у - 3 ху = - 7

{ 5 х + 3 ху = - 4

{ у - 3 ху = - 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}