已知AB=AD,∠BAD=100°所以∠ADB=40°,即∠DAC+∠DCA=40°且DC=2AD由正弦定理：sin∠DAC/sin∠DCA=CD/AD=2所以,sin∠DAC/sin(40°-∠DAC)=2化简得到：2sin40°*cos∠DAC=(1+2cos40°)*sin∠DAC得tan∠DAC=2sin40°/(...