Question 430415
3x^2+11xy-4y^2
= 3x^2+12xy-xy-4y^2
= 3x(x+4y)-y(x+4y)
= (3x-y)(x+4y)

10y^2+9y+2
=10y^2+5y+4y+2
=5y(2y+1)+2(2y+1)
=(5y+2)(2y+1)

12x^2-8x-15
=12x^2-18x+10x-15
=6x(2x-3)+5(2x-3)
=(6x+5)(2x-3)