Angle Inequalities in a Folded Right Triangle

Problem

figure

In ABC\triangle ABC, C=90\angle C=90^\circ, AC=1AC=1, BC=3BC=\sqrt{3}, and DD is the midpoint of side ABAB. A point MM lies on segment BDBD (excluding its endpoints). Triangle BCMBCM is folded up along CMCM to BCM\triangle B'CM. Let α\alpha be the dihedral angle between plane BCMB'CM and plane ACMACM, let β\beta be the angle between line MBMB' and plane AMCAMC, and let γ\gamma be the angle between line MCMC and plane BCAB'CA. During the folding, determine, with proof, which of the following statements are true:

(1) tanβ32tanα\tan\beta\leqslant\dfrac{\sqrt{3}}{2}\tan\alpha.

(2) γβ\gamma\leqslant\beta.

(3) γ>α\gamma>\alpha.

Answer

Solution

Difficulty8/10
Topicssolid geometry, Trigonometric Identities, Triangle Geometry

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