Question

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已知xy=-8,xy(x+y)=-16,求x的二次方+y的二次方的值

Answer 1

xy=-8,
xy(x+y)=-16
-8(x+y)=-16
(x+y)=2
(x+y)²=4
x²+y²+2xy=4
x²+y²=4-2xy
x²+y²=4+16
x²+y²=20

Answer 2

将xy代入得
(X+Y)=2
两边平方可得结果

Answer 3

x+y=2，x^2+y^2=(x+y)^2-2xy=4-2×(-8)=20