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Problem 18 - Entrance Test

If tan θ = 3/4 and θ is acute, find cos 2θ.

Correct: A

cos 2θ = (1 - tan^2 θ)/(1 + tan^2 θ) = (1 - 9/16)/(1 + 9/16) = (7/16)/(25/16) = 7/25.