=2根号3*(sin12/2cos12-根号3/2)/2sin12cos24 =2根号3(sin12cos60-cos12sin60)/2cos12sin12cos24 =2根号3sin(12-60)/2cos12sin12cos24 =2根号3sin48/sin24cos24 =4根号3sin48/sin48 =4根号3.
