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20 14 mathematical answers to Anqing's second model
Answer: (1) Proof: ∵ AC = 2, BC = 4, AB = 25, ∴ ∵AC=2+BC2 = AB=25, ∴AC⊥BC.

∫ plane PAC⊥ plane ABC, plane PAC∩ plane ABC=AC,

∴BC⊥ Plane packaging,

∵PA? Flat packaging, British Columbia, Pennsylvania ... (6 points)

(2) solution: let AD⊥PC be at point D. From the formula (1), we can know the bc⊥ flat packaging of BC⊥pc. ∴bc⊥ad.

PM∑BC and BC=2PM=4. The quadrilateral BCPM is a right-angled trapezoid with upper and lower bottoms of 2 and 4, height of 2 and area of 6 respectively.

BC∩PC=C, ∴AD⊥ plane BCPM, ad = 3.

Therefore, the volume of polyhedral PMBCA is13× sbcpm× ad =13× 6× 3 = 23 ... (13 minutes).