因为AD,CD是△ABC的两个外角的角平分线
所以∠DAC=∠EAD=1/2∠EAC
∠ACD=∠DCF=1/2∠ACF
且∠ADC=180°-∠DAC-∠ACD
=180°-1/2∠EAC-1/2∠ACF
=180°-1/2(180°-∠BAC)-1/2(180°-∠ACB)
=180°-90°+1/2∠BAC-90°+1/2∠ACB
=1/2∠BAC+1/2∠ACB
=1/2(∠BAC+∠ACB)
又因为∠BAC+∠ACB=180°-∠B=138°
所以∠ADC=69°
(过程是搬来的)
有不懂的可以问哦~