已知(x+y)²=36,(x-y)²=28,求(1)x²+y²的值,(2)xy的值

问题描述:

已知(x+y)²=36,(x-y)²=28,求(1)x²+y²的值,(2)xy的值

(x+y)²=36
x^2+2xy+y^2=36 (1)
(x-y)²=28
x^2-2xy+y^2=28 (2)
(1)+(2)得
x^2+y^2=32
(1)-(2)得
xy=2