2x的3次方减去0.5xy的3次方-2/3xy的3次方-xy的3次方-0.25x的3次方y
=2x³-0.5xy³-2/3xy³-xy³-0.25x³y
=2x³-1/2xy³-5/3xy³-0.25x³y
=2x³-3/6xy³-10/6xy³-0.25x³y
=2x³-13xy³-1/4x³y