18a^2-32b^2-18a+24b
=2(9a^2-16b^2)-6(3a-4b)
=2(3a-4b)(3a+4b)-6(3a-4b)
=2(3a-4b)[(3a+4b)-3]
=2(3a-4b)(3a+4b-3)y4-4y3+4y2-1y^4-4y^3+4y^2-1=y^4-1-4y^2(y-1)=(y^2+1)(y^2-1)-4y^2(y-1)=(y^2+1)(y+1)(y-1)-4y^2(y-1)=[(y^2+1)(y+1)-4y^2](y-1)=[y^3+y^2+y+1-4y^2](y-1)=(y^3-3y^2+y+1)(y-1)