证明:由勾股定理,PQ2=PM2+MQ2=PC2+QC2
(4AM )2=AC2+BC2
(AC-AP) 2+(BC-BQ) 2=PQ2
AC2-2AC*AP-2BC*BQ+BQ2+AP2+BC2=PQ2
PQ2=4AM2+PQ2-2AC*AP-2BC*BQ
2AM2=AC*AP+BC*BQ
=AC(AC-PC)+BC(BC-CQ)
=AC2+BC2-AC*PC-BC*CQ
=4AM2-AC*PC-BC*CQ
2AM2=AP*PC+BC*CQ
所以AP=PC,BQ=CQ
PQ2=PC2+QC2=AP2+BQ2