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calculate cosa in a tetrahedron, related to 2 midpoints

Source: IMAC Arhimede 2008 p4

May 4, 2019
geometry3D geometrytetrahedronmidpointstrigonometry

Problem Statement

Let ABCDABCD be a random tetrahedron. Let EE and FF be the midpoints of segments ABAB and CDCD, respectively. If the angle aa is between ADAD and BCBC, determine cosacos a in terms of EF,ADEF, AD and BCBC.
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