∫ x²arctanx dx= ∫ arctanx d(x³/3)= (1/3)x³arctanx - (1/3)∫ x³/(1+x²) dx,分部积分法= (1/3)x³arctanx - (1/3)∫ x(x²+1-1)/(1+x²) dx= (1/3)x³arctanx - (1/3)...