2x^2-xy-15y^2
=2x²-6xy+5xy-15y²
=2x(x-3y)+5y(x-3y)
=(x-3y)(2x+5y)
2x^2-5x-12
=2x²-8x+3x-12
=2x(x-4)+3(x-4)
=(x-4)(2x+3)