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3D Geometry Problem

Source: 1985 National High School Mathematics League, Exam Two, Problem 2

February 24, 2020
geometry3D geometry

Problem Statement

In cube ABCD−A1B1C1D1ABCD-A_1B_1C_1D_1, EE is midpoint of BCBC, F∈AA1F\in AA_1, and A1F:FA=1:2A_1F:FA=1:2. Calculate the dihedral angle between plane B1EFB_1EF and plane A1B1C1D1A_1B_1C_1D_1.
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