解:?$(1)∠A+∠D=∠C+∠B$?
?$(3)$?由?$(1)$?得?$∠DAP+∠D=∠P+∠DCP ①$?
?$∠PCB+∠B=∠PAB+∠P ②$?
由①+②,得?$∠DAP+∠D+∠PCB+∠B=∠P+∠DCP+∠PAB+∠P$?
∵?$∠DAB、$??$∠BCD$?的平分線?$AP$?和?$CP$?相交于點?$P$?
∴?$∠DAP=∠PAB,$??$∠DCP=∠PCB,$?即?$2∠P=∠D+∠B$?
∵?$∠D=40°,$??$∠B=36°$?
∴?$2∠P=76°$?
∴?$∠P=38°$?
?$(4)2∠P=∠D+∠B$?