已知(x+y)^2=20,(x-y)^2=40求①x^2+y^2② xy的值
问题描述:
已知(x+y)^2=20,(x-y)^2=40求①x^2+y^2② xy的值
答
(x+y)^2 + (x-y)^2=2x^2+2y^2=60
x^2+y^2=30
(x+y)^2 - (x-y)^2=4xy=-20
xy=-5