已知:如下图,DG⊥BC,AC⊥BC,EF⊥AB,∠1=∠2,求证:CD⊥AB。证明:∵DG⊥BC,AC⊥BC(已知)∴∠DGB=∠ACB=90°(垂直定义)∴DG∥AC( )∴∠2=( )( )∵∠1=∠2(已知)∴∠1=∠( )(等量代换)∴EF∥CD( )∴∠AEF=∠( )( )∵EF⊥AB(已知)∴∠AEF=90°( )∴∠ADC=90°( )∴CD⊥AB( )