1/(x^2+11x-8)+1/(x^2+2x-8)+1/(x^2-13x-8)=0
(x^2-8+2x)(x^2-8-13x)+(x^2-8+11x)(x^2-8-13x)+(x^2-8+11x)(x^2-8+2x)=0
(x^2-8)^2-11x(x^2-8)-26x^2+(x^2-8)^2-2x(x^2-8)-143x^2+(x^2-8)^2+13x(x^2-8)+22x^2=0
3(x^2-8)^2-147x^2=0
(x^2-8)^2-49x^2=0
(x^2+7x-8)(x^2-7x-8)=0
(x+8)(x-1)(x-8)(x+1)=0
x1=1, x2=-1, x3=8, x4=-8