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Right triangle ABC is base of pyramid ABCD, AD=BD and AB=CD

Source:

February 2, 2011

geometry3D geometrypyramidgeometry proposed

Problem Statement

Triangle

ABC

with

\angle BAC=90^{\circ}

is the base of the pyramid

ABCD

. Moreover,

AD=BD

and

AB=CD

. Prove that

\angle ACD\ge 30^{\circ}