3.Trigonometrical Ratios, Functions and Identities
hard

यदि $A, B, C$ धनात्मक न्यूनकोण इस प्रकार हैं कि  $A + B + C = \pi $ तथा $\cot A\,\cot \,B\,\cot \,C = K,$ तब

A

$K \le \frac{1}{{3\sqrt 3 }}$

B

$K \ge \frac{1}{{3\sqrt 3 }}$

C

$K < \frac{1}{9}$

D

$K > \frac{1}{3}$

Solution

$A + B + C = \pi $

$ \Rightarrow \tan A + \tan B + \tan C = \tan A\tan B\tan C$

अब समान्तर माध्य $\ge$ गुणोत्तर माध्य

$ \Rightarrow \frac{{\tan A + \tan B + \tan C}}{3} \ge {(\tan A\tan B\tan C)^{1/3}}$

$ \Rightarrow \left( {\frac{{\tan A\tan B\tan C}}{3}} \right) \ge {(\tan A\tan B\tan C)^{1/3}}$

$ \Rightarrow {(\tan A\tan B\tan C)^{2/3}} \ge 3$

$ \Rightarrow {\left( {\frac{1}{K}} \right)^{2/3}} \ge 3$

$\Rightarrow \frac{1}{K} \ge {3^{3/2}} $

$\Rightarrow K \le \frac{1}{{3\sqrt 3 }}$.

Standard 11
Mathematics

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