求(3x^4+2x^2)/(x^2+1)的不定积分,然后我想问问这题的思路,怎么把分母划去,变为可以积分的形式

∫(3x^4+2x^2)/(x^2+1)dx=∫(3x^4+3x^2-x^2)/(x^2+1)dx=∫[3x^2-x^2/(x^2+1)]dx=∫[3x^2-(x^2+1-1)/(x^2+1)]dx=∫[3x^2-1+1/(x^2+1)]dx=x^3-x+arctanx+C注意：分母是划不去的,像这类题,就是在分子上凑分母,然后约分,...