Question

当X ,Y 为何值时 -x的平方-2xy-2x+8y-5有最大值

Answer 1

2x + x^2 + 2y^2 + 2 + 2xy = 0

x^2 + 2(y + 1)*x + 2(y^2 + 1) = 0

K = 4(y + 1)^2 - 8(y^2 + 1)

= 4(y^2 + 2y + 1) - 8(y^2 + 1)

= -4y^2 + 8y - 4

= -4(y^2 - 2y + 1)

= -[2(y - 1)]^2 >= 0

y = 1

x^2 + 4x + 4 = 0

x = -2

x + y = -1 .A