求不定积分的解

分部积分：
∫ln(1+x^2)dx
=xln(1+x^2)-∫2x^2/(1+x^2)dx
=xln(1+x^2)-[∫2dx-∫2/(1+x^2)dx]
=xln(1+x^2)-2x+2arctanx+C
∫arccosxdx
=xarccosx-∫xd(arccosx)
=xarccosx+∫x/√(1-x^2)dx
=xarccosx-1/2∫(1-x^2)^(-1/2)d(1-x^2)
=xarccosx-√(1-x^2)