∴PC⊥ airplane ABC,

∵AC？ Avic aircraft, ∴ PC ⊥ AC

(2) Solution: ∵PC⊥ Aircraft ABC, PC? Aircraft PCBM, aircraft PCBM, aircraft ABC,

As shown in the figure, if A is the extension line of AD perpendicular to BC in the plane ABC and D is the plane PCBM of AD⊥, then AD is the height of the triangular pyramid A-MBC.

∫≈≈ ACB =120, ∴∠ ACD = 60, and in right-angled triangular ADC, AD = ACSIN 60 = 1× 32.

S△BMC=S quadrilateral PCBM-S△MPC= 12(PM+BC)? PC- 12PM？ personal computer

= 12( 1+2)× 1- 12× 1× 1= 1

∴VB-MAC=VA-MBC= 13S△MBC？ AD=36

The volume of triangular pyramid B-MAC is 36.