x + y = 4 ⇒ x = 4 - y ⇒ y = 4 - x
xy = -12
(4 - y) y = -12
4y - y² = -12
y² - 4y - 12 = 0 ⇒ y² = 4y + 12
x (4 - x) = -12
4x - x² = -12
x² - 4x - 12 = 0 ⇒ x² = 4x + 12
x² + 5xy + y²
(4x + 12) + 5(-12) + (4y +12)
4x + 12 - 60 + 4y + 12
4(x + y) - 36
4 (4) - 36
16 - 36
-20
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x + y = 4 ⇒ x = 4 - y ⇒ y = 4 - x
xy = -12
(4 - y) y = -12
4y - y² = -12
y² - 4y - 12 = 0 ⇒ y² = 4y + 12
x (4 - x) = -12
4x - x² = -12
x² - 4x - 12 = 0 ⇒ x² = 4x + 12
x² + 5xy + y²
(4x + 12) + 5(-12) + (4y +12)
4x + 12 - 60 + 4y + 12
4(x + y) - 36
4 (4) - 36
16 - 36
-20