1815                                     AB  M    CD EF   ED CF   AB P Q   MP=MQ                                                               
                                
   158  1973                                                                
AM=MB=α MQ=x  PM=y    ΔEPM ΔCMQ ΔDMP ΔFMQ   S1 S2 S3 S4   
   ∨E=∨C  ∨D=∨F ∨EMQ=∨PMD ∨FMQ=∨PME
  S1/S2 S2/S3 S3/S4 S4/S1=1
     PE EM sinE/MC CQ sinC    MC MQ sinMQ/MP MD sinPMD     MD DP sinD/MF FQ sinF   MQ MF sinFMQ/ME PM sinPME=PE DP  MQ 2/CQ FQ  PM 2=1
    PE DP  MQ 2=CQ FQ  MP 2  
   CQ FQ=BQ QA
                                                       = a-x a+x 
                                                       =a2-x2
                                                                           PE DP=AP PB
                                                       =a-y a+y 
                                                       =a2-y2
a2-y2x2=a2-x2y2
∵x y      ∴x=y  PM=MQ  
       