2x的m次方减去2y的m+一次方加7乘x乘m+1次方减y的m加1次方的差减3乘x的m次方减2y的m次方的差
=2x^m-2y^m+1+7x^m+1-y^m+1-(3x^m-2y^m)
=9x^m-3y^m+1-3x^m+2y^m
=6x^m-3y^m+1+2y^m