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
答
(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