C= (8-10x)(8x-10)(18y-9)
= (64x-80-80x^2+100)(18y-9)
= 1152xy-576x-1440y+720-1440x^2y+720x^2+1800y-900
= 1152xy-576x+360y-180-680^2
D= (x-1)(x+1)(1-x)(1+x)
= (x^2-1)(1-x^2)
= x^2 - x^4 - 1 + x^2
= -x^4 + 2x^2 - 1
E= x+2-(x+2)(2+x)(y-x)
= x+2(1-x+2)(y-x)
= x+2(y-x-xy+x^2+2y-2x)
= x+2(x^2-xy-3x+3y)
= x^3-x^2y-3x^2+3xy+2x^2-2xy-6x+6y
=x^3-x^2y-x^2+xy-6x+6y
