1.x^2+25xy+150y^2
=(x+15y)(x+10y);
2.(x+1)(x+2)-x-10
=x^2+3x+2-x-10
=x^2+ 2x-8
=(x+4)(x-2);
3.x^2-3xy-18y^2-3x-9y
=(x+3y)(x-6y)-3(x+3y)
=(x+3y)(x-6y-3).