hasnt this been posted before?
anyhow:
1) the pentagon is quite a bit taller than you'd think by seeing these images, therefore the hole is a lot bigger
2) the pentagon is supported by a metal matrix construction to toughen up the building
3) the outer ring of the pentagon is reinforced with kevlar to prevent flying pieces of rubble to become shrapnel and injuring people
4) as the plane hit, the wings broke and hit the hull. they got pulled into the building. (did you see a falling wing at the WTC ? i think not)
5) it is said the outer rings windows are bulletproof thereby allowing them to survive the shockwave of the impact.
(all above facts have been confirmed, except the windows)