2y^2-18=2*(y^2-9)=2*(y-3)*(y+3)
2x^2-12x+18=2*(x^2-6x+9)=
2*(x-3)^2=2*(x-3)*(x-3)
(2a+3)*(a-3)-2a*(4+a)=
2a^2+3a-6a-9-8a-2a^2=
-11a-9
(1-x)(x+1)+(x-1)^2=
(x-1)^2-(x-1)(x+1)=
(x-1)*(x-1-x-1)=
-2*(x-1)=
2-2x
x^4-27x=(x^2-3x)(x^2+3x+9)
x^4-27x=x^4-3x^3+3x^3-9x^2+9x^2-27x
x^4-27x=x^4-27x