`(2x+3y-4)(x-2y-3)=`

`2x*x+2x*(-2y)+2x*(-3)+3y*x+3y*(-2y)+3y*(-3)-4*x-4*(-2y)-4*(-3)=`

`2x^2-4xy-6x+3xy-6y^2-9y-4x+8y+12=`

`2x^2-6y^2-xy-10x-y+12`

`(2x+3y-4)(x-2y-3)=`

`2x*x+2x*(-2y)+2x*(-3)+3y*x+3y*(-2y)+3y*(-3)-4*x-4*(-2y)-4*(-3)=`

`2x^2-4xy-6x+3xy-6y^2-9y-4x+8y+12=`

`2x^2-6y^2-xy-10x-y+12`