求解几道解分式的题!(过程)谢!!

(1)x+y/x^3-y^3 +2y/y^3-x^3
=(x+y-2y)/(x^3-y^3)
=(x-y)/[(x-y)(x^2+xy+y^2)]
=1/(x^2+xy+y^2)

(2)(1-4x)^2/2x+3 乘 4x^2+12x+9/4x-1

=(4x-1)^2/(2x+3)*(2x+3)^2/(4x-1)

=(4x-1)(2x+3)

(3)x+2/x+1 - x+3/x+2 - x-4/x-3 + x-5/x-4

=[(x+1)+1]/(x+1)-(x+2+1)/(x+2)-(x-3-1)/(x-3)+(x-4-1)/(x-4)

=1+1/(x+1)-1-1/(x+2)-1+1/(x-3)+1-1/(x-4)

=(x+2-x-1)/(x+1)(x+2)+(x-4-x+3)/(x-3)(x-4)

=1/(x+1)(x+2)-1/(x-3)(x-4)

=(x^2-7x+12-(x^2+3x+2))/(x+1)(x+2)(x-3)(x-4)

=-10(x-1)/(x+1)(x+2)(x-3)(x-4)