（3X²+2Xy-1/2x）-﹙2x²-xy+x﹚
=3x²+2xy-1/2x-2x²+xy-x
=x²+3xy-3/2x
﹙1/2xy+y²+1﹚+﹙x²-1/2xy-2y²-1﹚
=1/2xy+y²+1+x²-1/2xy-2y²-1
=x²-y²
-﹙x²y+3xy-4﹚+3﹙x²y-xy+2﹚
=-x²y-3xy+4+3x²y-3xy+6
=2x²y-6xy+10
-1/4﹙2k ³-2k ²+4k﹚
=-1/2k³+1/2k²-k