(2-4cos^212度)/[csc12度(3-根号3tan12度)]
=-2cos24/[csc12度(3-根号3tan12度)]
=-2sin12cos24/(3-根号3tan12度)
=-√3cos12sin12cos24/(√3/2*cos12-1/2*sin12)
=-√3/2*sin24cos24/sin(60-12)
=-√3/4*sin48/sin48
=-√3/4