2016年3月山东省滨州市八年级下段考数学试卷含答案解析  
9．如图，在Rt△ABC中，AB⊥AC，AD是斜边上的高，DE⊥AC，DF⊥AB，垂足分别为E，F，则图中与∠C（∠C除外）相等的角的个数是（　　）                                                                      
A．1个         B．2个         C．3个        D．4个
【考点】余角和补角．                                                                        
【专题】计算题．                                                                               
【分析】利用垂直得到∠CDE=∠AFD=90°，然后利用等角的余角相等找出与∠C（∠C除外）相等的角．                     
【解答】解：∵DE⊥AC，                                                                       
∴∠CDE=90°，                                                                                  
∴∠C+∠CDE=90°，∠CDE+∠ADE=90°，                                               
∴∠ADE=∠C，                                                                                 
∵DE∥AB，                                                                                       
∴∠ADE=∠BAD，                                                      
∴∠C=∠BAD，                                                                                 
∵FD⊥AB，                                                                                       
∴DF∥AC，                                                                                       
∴∠BDF=∠C．                                                                                  
故选C．                                                                                             
【点评】本题考查了余角和补角：如果两个角的和等于90°（直角），就说这两个角互为余角．即其中一个角是另一个角的余角．如果两个角的和等于180°（平角），就说这两个角互为补角．即其中一个角是另一个角的补角．