x³+y³=10,x²-xy=﹣3
﹙x³-y³﹚-﹙2x²-4xy²﹚-2﹙﹣y³+xy²﹚
=x³-y³-2x²+4xy²+2y³-2xy²
=﹙x³+y³﹚-2﹙x²-xy²﹚
=10-2×﹙﹣3﹚
=16.