Published by:
CGP EDU Academic Team
Published on: August 14, 2026
In a regular tetrahedron let θ be the angle between any edge and a face not containing the edge.
If cos2 θ = 
where a, b ∈ I+ also a and b are coprime, then find the value of 
(10a + b)
Text Solution
Verified by ExpertsThe correct answer is:
5
Ans. 5
Sol. coprime, then find the value of 
(10a + b)
Let OABC be the tetrahedron. Let G be the
entroid of the face OAB, then GA = 
AC.
Then cos θ = 
∴ cos2 θ = 
∴ a = 1 and b = 3
∴ 10 a + b = 13
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