x^2-4x+4=0
(x-2)^2=0
x=2
2y^2+12y+18=0
2(y^2+6y+9)=0
2(y+3)^2=0
y=-3
9x^2-12xy+4y^2
=(3x-2y)^2
=[3×2-2×（-3）]^2
=12^2=144
m^6-1
=(m^3+1)(m^3-1)
=(m-1)(m^2+m+1)(m+1)(m^2-m+1)