证明:原式=(x5+3x4y)-(5x3y2+15x2y3)+(4xy4+12y5)
=x4(x+3y)-5x2y2(x+3y)+4y4(x+3y)
=(x+3y)(x4-5x2y2+4y4)
=(x+3y)(x2-4y2)(x2-y2)
=(x+3y)(x-2y)(x+2y)(x+y)(x-y)
当y=0时,原式=x5≠33;
当y≠0时,x+3y、x-y、x+y、x-2y、x+2y互不相同,而33不可能分解为3个以上不同因数的积
所以x5+3x4y-5x3y2-15x2y3+4xy4+12y5的值不会等于33.