Problem

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Tags: geometry, 3D geometry, cube, angles, parallel, equal segments



In the rectangular parallelepiped ABCDABCD we denote by M the center of the face ABBA. We denote by M1 and M2 the projections of M on the lines BC and AD respectively. Prove that: a) MM1=MM2 b) if (MM1M2)(ABC)=d, then dAD; c) (MM1M2),(ABC)=45oBCAB=BBBC+BCBB.