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Value of cot⁡{π4−2cot⁡−13}\cot\left\{\frac{\pi}{4} - 2\cot^{-1}3\right\} is

Solution

✅ Correct Option: 3

Let θ=cot⁡−13\theta=\cot^{-1}3, so tan⁡θ=13\tan\theta=\frac13 and tan⁡2θ=2/31−1/9=34\tan2\theta=\frac{2/3}{1-1/9}=\frac34. Then tan⁡(π4−2θ)=1−3/41+3/4=17\tan\left(\frac{\pi}{4}-2\theta\right)=\frac{1-3/4}{1+3/4}=\frac17, so the cotangent is 7.

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