3D Trigonometry pass paper (HKCEE 1999 )

In the figure, ABC is an equilateral triangle of side 24 cm and BD = DE = EF = FC. It is folded to form an aeroplane by dragging the red point so that D and F coincide. The aeroplane is supported by two vertical sticks BM and CN so that A,B, D, F, C lie on the same plane. (a) Find the distance between the tips, B and C, of the wings of the aeroplane. (b) Find the inclination of the wings of the aeroplane to the horizontal ground. (c) Find the length of the stick CN.

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