3a^2-b）-a（3b-4）
=6a^2-2b-3ab+4a
=2a(3a+2)-b(3a+2)
=(2a-b)(3a+2)
m^2-3m+1=0,求m^2+1/m^2
m^2-3m+1=0
m-3+1/m=0
m^2+1/m^2=(m+1/m)^2-2=3^2-2=7