计算不定积分∫[dx/(9+4x2)]．

计算不定积分∫[dx/(9+4x2)]．
【正确答案】：∫[dx/(9+4x2)]=∫{dx/9[1+((2/3)x)2]} =∫{(3/2)d[(2/3)x]/9[1+((2/3)x)2]} =(1/6)arctan(2/3)x+C．