原式=-2M(M^4-1)=-2M(M^2+1)(M^2-1)=-2M(M^2+1)(M+1)(M-1)
2m-2m^5=2m(1-m^4)=2m(1+m^2)(1-m^2)=2m(1+m^2)(1+m)(1-m)
