MCQ
If $\tan A + \cot A = 4,$ then ${\tan ^4}A + {\cot ^4}A$ is equal to
  • A
    $110$
  • B
    $191$
  • C
    $80$
  • $194$

Answer

Correct option: D.
$194$
d
(d) $\tan A + \cot A = 4$ 

$ \Rightarrow \,{\tan ^2}A + {\cot ^2}A + 2\,\tan A\,\,\cot A = 16$

$ \Rightarrow \,{\tan ^2}A + {\cot ^2}A = 14\,\, $

$\Rightarrow \,{\tan ^4}A + {\cot ^4}A + 2 = 196$

$ \Rightarrow \,{\tan ^4}A + {\cot ^4}A = 194.$

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