X² + Y² = (X² + 2*X*Y + Y²) - 2*X*Y = (X + Y)² - 2*X*Y = 12² - 2*1 = 144 - 2 = 142
(3xy² + 5x²y² - 7xy + 7 + 11) + (- 2xy² + x²y² + 2xy + y - 2) =
= <u>3xy²</u> + 5x²y²<em> - 7xy</em> + 18 - <u>2xy²</u> + x²y² <em>+2xy</em> + y - 2 =
= 6x²y² + xy² - 5xy + y + 16
(x^2 + 6x)^2 + 2(x^2 + 6x + 9) - 81 = 0
x^2 + 6x = a,
x^2 +6x + 9 = a + 9,
a^2 + 2(a + 9) - 81 = 0,
a^2 + 2a - 63 = 0
а1 = -9
a2 = 7
x^2 + 6x = -9
x^2 + 6x + 9 = 0
x = -3
x^2 + 6x = 7
x^2 + 6x -7 = 0
x1 = -7
x2 = 1
ответ. -7; -3; 1.