如图,AD∥BC ,∠D=100,CA平分∠BCD,则∠DAC?

如图,AD∥BC ,∠D=100,CA平分∠BCD,则∠DAC?
如图,AD∥BC ,∠D=100,CA平分∠BCD,则∠DAC?
 

如图,AD∥BC ,∠D=100,CA平分∠BCD,则∠DAC?
∵AD∥BC
∴∠D＋∠DCB=180°
又∵∠D=100°
∴∠DCB=80°
又∵AC平分∠DCB
∴∠ACD=∠ACB=40°
又∵AD∥BC
∴∠DAC=∠ACB=40°

因为CA平分∠BCD,所以∠BCA=∠DCA
因为AD//BC，所以∠BCA=∠DAC=∠DCA,所以∠DAC=(180-100)/2=40

40

dac=acbalternate interior angle.恩 知道呢 ∠D=100º 那∠DAC呢?dac = d