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← JEE Main 2022 · 28 Jul · Shift 2
MathematicsInteger+4 / -1Question 87 of 90

JEE Main 2022 · 28 Jul · Shift 2, Mathematics question 87

Let S=[−π,π2)−{−π2,−π4,−3π4,π4}S=\left[-\pi,\dfrac\pi2\right)-\left\{-\dfrac\pi2,-\dfrac\pi4,-\dfrac{3\pi}4,\dfrac\pi4\right\}. Then the number of elements in the set A={θ∈S:tan⁡θ(1+5tan⁡(2θ))=5−tan⁡(2θ)}A=\left\{\theta\in S:\tan\theta\left(1+\sqrt5\tan(2\theta)\right)=\sqrt5-\tan(2\theta)\right\} is ______.

Answer and worked solution

Official answer: 5

Rearrange to tan⁡3θ=5\tan3\theta=\sqrt5, so 3θ=α+kπ3\theta=\alpha+k\pi in [−3π,3π2)[-3\pi,\frac{3\pi}2) with α=tan⁡−15\alpha=\tan^{-1}\sqrt5.

k=−3,…,1k=-3,\dots,1: 5 values, none excluded.

Answer: 5