Because Pb ⊥ PE ∠ GPB+∠ FPE = 90 ∠ GBP = ∠ FPE ∠ PGB = ∠ PFE = 90.
So △PGB=△EFP, so EF=GP=GA=DF.
②CE=CF-EF=PC/ radical number two -PA/ radical number two, so PC=PA+ radical number two CE.
(2)DF-EF is still valid. The same method as above is still full of certificates.
PA=PC+ root sign CE