Math Is Fun Forum

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Repeat the procedure with the triangular face adjacent to the sloping edge containing the point N. Draw the perpendicular from the vertex to the midpoint L of the base; then LN is perpendicular to the sloping edge and |LN| = d.

And angle MNL is the angle between the two faces; it’s what you need to calculate. Consider triangle MNL. You have |MN| = |LN| = d and |ML| =

. So calculate ∠MNL.