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Math triangle proof problem in the first day of junior high school.
1. Proof: Take point E on the extension line of BA, make AE = AC, and then connect PE.

Advertising dichotomy ∠CAE

∴∠CAD=∠EAD

AE = AC,AP=AP

∴△AEP≌△ACP

∴PE=PC

∫in△BPE:p b+ PC > Be,Be = AB+AE = AB+AC。

∴PB+PC>AB+AC

2. Proof: Take point E of AC side to make AE = AB, and then connect PE.

Advertising dichotomy ∠CAE

∴∠CAD=∠BAD

AE = AB,AP=AP

∴△AEP≌△ABP

∴PE=PB

∫In△BPE:PC-PE < CE,CE = AC-AE = AC-AB。

∴PC-PB