3*Y^2-6*X*Y-9*X^2=3*(Y*Y-2*X*Y-3*X*X)
3y^2-6xy-9x^2=3(y^2-2xy-3x^2)=3(y^2+xy-3xy-3x^2)=3(y(y+x)-3x(y+x))=3(y+x)(y-3x)
3*Y^2-6*X*Y-9*X^2=3*(Y*Y-2*X*Y-3*X*X)
3y^2-6xy-9x^2=3(y^2-2xy-3x^2)=3(y^2+xy-3xy-3x^2)=3(y(y+x)-3x(y+x))=3(y+x)(y-3x)