سیگما

`Q=int root3((x+1)/(x-1)) dx`
`t^3=(x+1)/(x-1)`
`x=(t^3+1)/(t^3-1)`
`(dx)/(dt)=(-6t^2)/(t^3-1)^2`
`Q=-int (6t^3)/(t^3-1)^2 dt`
`(6t^3)/(t^3-1)^2=A/(t-1)+B/(t-1)^2+(Cx+D)/(t^2+t+1)+(Ex+F)/(t^2+t+1)^2`
`A=2/3,B=2/3,C=-2/3,D=-2,E=2,F=2`
`Q=-int (2t+2)/(t^2+t+1)^2-(2t+6)/(3(t^2+t+1))+2/(3(t-1))+2/(3(t-1)^2) dt`
`Q=1/3((6t)/(t^3-1)+ln((t^2+t+1)/(1-t)^2)+2sqrt(3)arctan((2t+1)/sqrt(3)))`
`t=((x+1)/(x-1))^1/3`