4(cos12)^2-2
=2[2(cos12)^2-1]
=2cos24
所以分母=2cos24sin12
分子=√3*sin12/cos12-3
=(√3*sin12-3cos12)/cos12
所以原式=(√3*sin12-3cos12)/[cos12*2cos24sin12]
=(√3*sin12-3cos12)/[(1/2)*sin48]
=2(√3*sin12-3cos12)/sin48
=4√3[(1/2)sin12-√3/2*cos12)/sin48
=4√3(sin12cos60-cos12sin60)/sin48
=4√3(sin12-60)/sin48
=-4√3sin48/sin48
=-4√3