原式=1/2∫(0→1)arctanxd(x^2)=1/2x^2arctanx|(0→1)-1/2∫(0→1)x^2*1/(1+x^2)dx=1/2x^2arctanx|(0→1)-1/2∫(0→1)(x^2+1-1)/(x^2+1)dx=1/2x^2arctanx|(0→1)-1/2∫(0→1)dx+1/2∫(0→1)dx/(x^2+1)=1/2x^2arctanx...