Published by:
CGP EDU Academic Team
Published on: August 14, 2026
The value of sec 3 θ , where θ is the acute angle between the plane faces of a regular tetrahedron, is
Text Solution
Verified by ExpertsThe correct answer is:
27
(27)
Sol. Since tetrahedron is regular AB = BC = AC = DC and angle between two adjcant side = π /3
consider planes ABD and DBC vector, normal to plane ABD is = 
vector, normal to plane DBC is = 
angle between these planes is angle between
vectors 
& 
⇒ 
= 
= 
Since acute angle is required 
⇒ sec θ = 3 ⇒ sec 3 θ = 27
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