If cot−1(n2−10n+21.6π)>π6,nϵN terms, then n can be
A
3
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B
2
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C
4
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D
8
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Solution
The correct options are A 4 B 3 Taking cot on both the sides, we get n2−10n+21.6<πcot(π6) ...( inequality sign gets reversed, since cot(x) is a decreasing function). n2−10n+21.6<π(√3) n2−10n+21.6<5.44 n2−10n+16.19<0 Consider g(n)=n2−10n+16.19 g(2)=4−20+16.19 =0.19 ...(i) g(3)=9−30+16.19 =−4.81<0 ...(ii) g(4)=16−40+16.19 =−7.81<0 ...(iii) g(8)=64−80+16.19 =0.19 ...(iv) Hence only 3, and 4 satisfies the above inequality,