∵AB=AC∴∠B=∠C∵AC=CD∴∠CAD=∠CDA=(180°-∠C)/2=90°-1/2∠B∵AD=BD∴∠DAB=∠B∵∠BAC=∠DAB+∠CAD=∠B+90°-1/2∠B=90°+1/2∠B∴∠B+∠BAC+∠C=180°即∠B+90°+1/2∠B+∠B=180°∠B=∠C=36°∴∠BAC=180°-∠B-∠C=180°-36°-36°=108°
