(1) -2x的2次方—4x的n次方
=-2x²(1+2x的n-2次方)
(2)x(a-b)的2n次方+xy(b-a)的2n+1次方
=x(a-b)的2n次方-xy(a-b)的2n+1次方
=x(a-b)的2n次方(1-ya+yb)