∵EF⊥AB∴∠AEF=90°∵DG⊥BC，AC⊥BC∴DG∥AC∴∠2=∠DCA（两直线平行，内错角相等）∵∠1=∠2∴∠1=∠DCA∴EF∥CD(同位角相等，两直线平行）∴∠AEF=∠ADC=90°∴CD⊥AB
证明：∵DG∥BC∴∠1=∠DCE∵CD⊥AB,EF⊥AB∴DC∥FE∴∠2=∠DCE∵∠1=∠DCE∠2=∠DCE∴∠1=∠2
