( 1)。 Prove AC vertical de; (2)。 If PC=√2? BC finds the cosine of dihedral angle e-ac-p.
Solution: (1). Proof: ∵PD⊥ plane ABCD, AC? Aircraft ABCD, ∴ AC ⊥ PD; Connect BD, ABCD is square,
∴ac⊥bd; Therefore, AC⊥ aircraft pdb;; De? Plane pdb aircraft
(2)。 Let the intersection of two diagonal lines of the bottom square ABCD be O. Connect PO and EO; ∵PD⊥ plane ABCD, PD=PD,
AD=CD, ∴RT△PDA≌RT△PDC, ∴AP=CP, that is, △PAC is an isosceles triangle; O is the midpoint of AC, so po
⊥ac; It turns out that AC⊥ aircraft PDB, EO? Planar PDB, ∴ EO ⊥ AC; So ∠POE is the flatness of dihedral angle e-AC-p.
Face angle.
∫PC =√2? BC=√2? cd,∴∠pcd=45; Let PD=CD= 1, then BD = √ 2; PB? =PD? +BD? = 1+2=3;
PE =(2/3)PB =(2/3)√3; Po. =PD? +DO? = 1+ 1/2=3/2; BE =( 1/3)PB =( 1/3)√3; BO = BD/2 =√2/2;
cos∠PBD = BD/PB =√(2/3);
EO? = Bo? +BE? -2BO? Bekos ∠ PBD =1/2+(1/3)-2× (√ 2/2) × (√ 3/3 )× √ (2/3) =1/6;
So cos∠POE=(PO? +EO? -Sports? )/(2po×EO)=(3/2+ 1/6-4/3)/[2×√( 3/2)×√( 1/6)]= 1/3。