过E做EH垂直AB交AB于H;
∵CD⊥BC;EH⊥AB;
又∵BE平分∠ABC;
∴EC=EH;
∵E是CD的中点;
∴DE=EC;
∴DE=EH;
∵AD//BC
∴AD⊥CD;
∵EH⊥AB;
∴AE平分∠BAD