原式=(x-1)(x^2+x+1)/[(x+1)(x^2+x+1)]+(x+1)(x^2-x+1)/[(x-1)(x^2-x+1)]-(2x^2+2)/(x^2-1)
=(x-1)/(x+1)+)]+(x+1)/(x-1))-(2x^2+2)/(x^2-1)
=[(x-1)^2+(x+1)^2-(2x^2+2)/]/(x^2-1)
=0.
原式=(x-1)(x^2+x+1)/[(x+1)(x^2+x+1)]+(x+1)(x^2-x+1)/[(x-1)(x^2-x+1)]-(2x^2+2)/(x^2-1)
=(x-1)/(x+1)+)]+(x+1)/(x-1))-(2x^2+2)/(x^2-1)
=[(x-1)^2+(x+1)^2-(2x^2+2)/]/(x^2-1)
=0.