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midpoint and perpendicular wanted in 3D, planes angle given, rectangle

Source: 2007 Romania District VIII P2

May 18, 2020
geometry3D geometryrectangleanglesrectnagleperpendicular bisectormidpoint

Problem Statement

Consider a rectangle ABCDABCD with AB=2AB = 2 and BC=3BC = \sqrt3. The point MM lies on the side ADAD so that MD=2AMMD = 2 AM and the point NN is the midpoint of the segment ABAB. On the plane of the rectangle rises the perpendicular MP and we choose the point QQ on the segment MPMP such that the measure of the angle between the planes (MPC)(MPC) and (NPC)(NPC) shall be 45o45^o, and the measure of the angle between the planes (MPC)(MPC) and (QNC)(QNC) shall be 60o60^o.
a) Show that the lines DNDN and CMCM are perpendicular.
b) Show that the point QQ is the midpoint of the segment MPMP.