A Frustum Dihedral

Problem

In a triangular frustum $ABC\text{-}DEF$ , $AB\perp AC$ , $AB=2DE=2$ , $AC=2\sqrt 2$ , $CF=2$ , and $CF$ is perpendicular to the plane $ABC$ . Let $P$ , $Q$ , $R$ be the midpoints of $AC$ , $FC$ , $BC$ respectively.

1. Prove that the plane $BCD$ is perpendicular to the plane $PQR$ . 2. Find the sine of the dihedral angle $E\text{-}BD\text{-}C$ .

Answer

Solution

Difficulty	7/10
Topics	solid geometry, Triangle Geometry

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