SA=SA, angle SAB= angle sad = 90, ab = ad.

therefore

δSAB?δSAD

AE is the height of Δ Δ SAB, and AF is the height of triangle SAD.

Yi Zhi SE=SF

Therefore, in Δ Δ SBD, ef is parallel to BD.

BD⊥SA,BD⊥AC

So BD⊥ Airbag,

So BD⊥SC

Because EF is parallel to BD

So EF⊥SC