以AB为边向AC一侧做等边三角形ABE,连接AE和CE,DE
∠A=20°
AB=AC
∠ABC=∠ACB=80°
∠BCE=20°
AE=AB=AC
∠BAE=60°∠CAE=40°
∠ACE=∠AEC=70°
∠BEC=70-60=10°
BC=AD AC=BE
∠CBE=∠BAC=20°
△ADC≌△BCE
∠ADC=∠BCE=150°
∠BDC=30°
以AB为边向AC一侧做等边三角形ABE,连接AE和CE,DE
∠A=20°
AB=AC
∠ABC=∠ACB=80°
∠BCE=20°
AE=AB=AC
∠BAE=60°∠CAE=40°
∠ACE=∠AEC=70°
∠BEC=70-60=10°
BC=AD AC=BE
∠CBE=∠BAC=20°
△ADC≌△BCE
∠ADC=∠BCE=150°
∠BDC=30°