图上21题,图上21题,
图上21题,
证明:∵AB=AD,CB=CD,AC=AC∴△ABC≌△ADC (SSS)∴∠ACB=∠ACD∵PE⊥BC,PF⊥CD∴∠PEC=∠PFC=90∵CP=CP∴△PCE≌△PCF (AAS)∴PE=PF