سیگما

`Q=int (dx)/(x^3+1)`
`Q=int (dx)/((x+1)(x^2-x+1))`
`Q=int A/(x+1)+(Bx+C)/(x^2-x+1)dx`
`A=1/3 , B=-1/3 , C=2/3`
`Q=1/3 int 1/(x+1)dx+int (-1/3x+2/3)/(x^2-x+1)dx`
`Q=1/3ln(x+1)-1/6int(2x-1-3)/(x^2-x+1)dx`
`Q=2/6ln(x+1)-1/6ln(x^2-x+1)+1/2int(dx)/(x^2-x+1)dx`
`Q=1/6ln|(x+1)^2|-1/6ln(x^2-x+1)+1/2int(dx)/((x-1/2)^2+3/4)dx`
`Q=(ln|(x+1)^2/(x^2-x+1)|)/6+1/sqrt(3)arctan((2x-1)/(sqrt(3)))`