AB=AC∠B=∠ACB=1/2(180°-∠BAC)=90°-1/2∠BAC∠ACD=1/2∠ACB=1/2(90°-1/2∠BAC)=45°-1/4∠BAC∠CAD+∠ACD+∠ADC=180°1/2∠BAC+45°-1/4∠BAC+130°=180°1/4∠BAC=5°∠BAC=20°
