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The value of tan⁡(12cos⁡−153)\tan\left(\dfrac{1}{2}\cos^{-1}\dfrac{\sqrt5}{3}\right) is equal to

Solution

✅ Correct Option: 4

Let θ=cos⁡−153\theta=\cos^{-1}\frac{\sqrt{5}}{3}, so cos⁡θ=53\cos\theta=\frac{\sqrt{5}}{3} and sin⁡θ=1−59=23\sin\theta=\sqrt{1-\frac{5}{9}}=\frac{2}{3}. Using tan⁡θ2=1−cos⁡θsin⁡θ\tan\frac{\theta}{2}=\frac{1-\cos\theta}{\sin\theta}, the value is 1−5323=3−52\frac{1-\frac{\sqrt{5}}{3}}{\frac{2}{3}}=\frac{3-\sqrt{5}}{2}.

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