若x(x+1)-(x^2+y)=-5,则 (x^2+y^2)/2-xy的值为
问题描述:
若x(x+1)-(x^2+y)=-5,则 (x^2+y^2)/2-xy的值为
答
x(x+1)-(x²+y)=-5
x-y=-5
( x-y)²=25
( x-y)²/2=12.5=(x²+y²)/2-xy