∫xarctanxdx=1/2 ∫arctanxdx^2=1/2[x^2arctanx|(0,1)-∫(0,1)x^2/(1+x^2)dx]=1/2[π/4-∫(0,1)1-1/(1+x^2)dx] =1/2[π/4-∫(0,1)dx+∫(0,1)1/(1+x^2)dx] =1/2[π/4-x|(0,1)+arctanx|(0,1)]=π/4-1/2