I=∫01cot−1(1+x+x2)dxI=∫01tan−1(1+x+x21)dxI=∫01tan−1(1+(x+1)x(x+1)−x)dxI=∫01(tan−1(x+1)−tan−1x)dxI=∫01tan−1(x+1)dx−∫01tan−1xdxSubstituting
x+1=t in the first integral:
I=∫12tan−1xdx−∫01tan−1xdxUsing integration by parts,
∫tan−1xdx=xtan−1x−21loge(1+x2)I=[xtan−1x−21loge(1+x2)]12−[xtan−1x−21loge(1+x2)]01I=(2tan−12−21loge5−(4π−21loge2))−(4π−21loge2−0)I=2tan−12−21loge5−2π+loge2I=2tan−12−21loge5+21loge4−2πI=2tan−12−21loge(45)−2πAnswer:
2tan−12−21loge(45)−2π