不定积：∫(x^4/(x^2+1))dx 忘了怎么解了.求高手帮下忙哈

x⁴/(x² + 1)= x²(x² + 1 - 1)/(x² + 1)= x² - x²/(x² + 1)= x² - (x² + 1 - 1)/(x² + 1)= x² - 1 + 1/(x² + 1)∫ x⁴/(x² + 1) dx= ∫ x² dx - ∫ dx + ∫ dx/(x² + 1)= (1/3)x³ - x + arctan(x) + C