y=x-3x+1经过点(m,0),
代入得到m^2-3m+1=0
m^2=3m-1
m4-21m+10
=(3m-1)^2-21m+10
=9m^2-6m+1-21m+10
=9m^2-27m+11
=9(3m-1)-27m+11
=-9+11