∴AD=AQ,∠QAD=90
Q is QE⊥PD, and PD is E.
PQC⊥ aircraft dcq;;
∴E is the midpoint of PD == >; QD=QP,QD⊥QP
CD⊥ Yi Zhi surface AQPD== >CD⊥PQ.
∴PQ⊥ surface dry quenching
PQC dry quenching
(2) Analysis: Let the side length of ABCD be 1.
It is easy to know the PCD of BC⊥ plane = = > BC ⊥ PC.
∴bc=cd= 1,pd=2==>; PC =√5 = = & gt; PB=√6
Go through c, CF⊥PB from PB to f, q, QG⊥PB from PB to g, f, HF//QG from QB to h, and connect HC.
∴∠CFH is the plane angle of dihedral angle Q-BP-C.
bc^2=bf*bp==>; 1 = BF *√6 = = & gt; BF=√6/6== >CF=√(BC^2-BF^2)=√30/6
Yi Zhi BQ=DQ=PQ=√2
∴G is the midpoint of PB
QG=√(BQ^2-BG^2)=√2/2
⊿bfh∽⊿bgq==>; Blast furnace/blast furnace = blast furnace /QG = blast furnace /BQ
∴HF=√2/6,BH=√2/3
∵BC⊥BQ
∴ch=√(bc^2+bh^2)=√ 1 1/3
According to the cosine theorem HC 2 = FC 2+FH 2-2 * FC * HF * COS ∠ CFH.
1 1/9 = 5/6+ 1/ 18-2 *√30/6 *√2/6 * cos∠CFH
cos∠CFH=-√ 15/5
∴ The cosine Q-BP-C of dihedral angle is -√ 15/5.