Question

已知A=x三次方+2y三次方-xy二次方，B=-y三次方+x三次方+2xy二次方，其中x=三分之一，y=2，求a-b的值

Answer 1

A-B=x³轮肆弊好+2y³-xy²-(-y³+x³+2xy²腊卜轿)
=x³+2y³-xy²+y³-x³-2xy²
=3y³-3xy²
=3*2³-3*1/3*2²
=24-4
=20

Answer 2

A-B=x³+2y³-xy²-(-y³+x³+2xy²)
=x³+2y³-xy²+y³-x³-2xy²槐滚
=3y³饥明判-3xy²烂改
=3y²(y-x)
=3*2*2*(2-1/3)
=20