已知m2次方+3m+1=0,
m^2=-3m-1
m3次方-8m的值
=m(m^2-8)
=m(-3m-1-8)
=-3m(m+3)
=-3m^2-9m
=-3(-3m-1)-9m
=9m+3-9m
=3=-3m^2-9m=-3(-3m-1)-9m？因为m^2=-3m-1所以=-3m^2-9m=-3(-3m-1)-9m等于说你用了两次：m^2=-3m-1对的，凡是m^2都可以等于-3m-1