∫rln(1+r2)dr
=(1/2)∫ln(1+r2)d(1+r2)
=(1/2)[(1+r2)ln(1+r2)-∫(1+r2)dln(1+r2)]
=(1/2)[(1+r2)ln(1+r2)-∫1dr]
=(1/2)(1+r2)ln(1+r2)-(r/2)