limx->0 (1-cosxcos2xcos3x)/(x^2) 罗必塔=limx->0 (sinxcos2xcos3x+2sin2xcosxcos3x+3sin3xcosxcos2x)/2x sinx~x=limx->0 (1/2cos2xcos3x+2cosxcos3x+3*3/2cosxcos2x) =7
