A tetrahedron has vertices ,

MATHEMATICS · Single correct · ISC · Mathematics · Three-Dimensional Geometry · Three-Dimensional Geometry

Problem

A tetrahedron has vertices O(0,0,0)O(0, 0, 0), A(1,2,1)A(1, 2, 1), B(2,1,3)B(2, 1, 3) and C(−1,1,2)C(-1, 1, 2). Then the angle between the faces OABOAB and ABCABC will be (1) cos⁡−1(1935)\cos^{-1}\left(\frac{19}{35}\right) (2) cos⁡−1(1731)\cos^{-1}\left(\frac{17}{31}\right) (3) 30∘30^\circ (4) 90∘90^\circ

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