∵AE平分∠BAC∴∠BAE=∠2∵CE平分∠ACD∴∠ECD=∠1∵∠1+∠2=90°∴∠ECD+∠BAE=∠1+∠2=90°∴∠BAC+∠ACD=∠ECD+∠BAE+∠1+∠2=90°+90°=180°∴CD//AB
