x﹙x-1﹚-﹙x²-y﹚=-2
x²-x-x²+y=-2
x-y=2
x²+y²／2-xy
=1/2*x²+1/2(x²-2xy+y²)
=1/2(x-y)²+1/2*x²
=1/2×2²+1/2*x²
=2 +1/2*x²
=