已知X(X-1)-(X²一y)=-2,求X²+y²/2-Xy的值

问题描述:

已知X(X-1)-(X²一y)=-2,求X²+y²/2-Xy的值
如上

X(X-1)-(X²一y)=-2
x²-x-x²+y=-2
∴-x+y=-2
即x-y=2
(x²+y²)/2-xy
=1/2(x²+y²-2xy)
=1/2(x-y)²
=2²÷2
=2