Question
If tan 4θ = cot 14θ, then find the value of cos 9θ.
Solution
tan 4θ = cot 14θ Or, tan 4θ = cot (90o - 4θ) [because, tan A = cot (90o - A) ] Or, 14θ = 90o - 4θ Or, 18θ = 90o Or, θ = (90/18) o = 5o So, cos 9θ = cos 45o = (1/√2)
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