Sorry( ma fault. Actually it was (x+1)/(x^2+x+1) and I divided it into two fractions. They are (2x+1)/(x^2+x+1) and 1/(x^2+x+1). I solved first fraction, but I do not know what to do whith second fraction. I wrote something, can you check it?please. Is it right? I used as you said trig substitution .