Medium MCQ +4 / -1 PYQ · JEE Mains 2021

The number of solutions of the equation ${32^{{{\tan }^2}x}} + {32^{{{\sec }^2}x}} = 81,\,0 \le x \le {\pi \over 4}$ is :

  1. A 3
  2. B 1 Correct answer
  3. C 0
  4. D 2

Solution

${(32)^{{{\tan }^2}x}} + {(32)^{{{\sec }^2}x}} = 81$<br><br>$\Rightarrow {(32)^{{{\tan }^2}x}} + {(32)^{1 + {{\tan }^2}x}} = 81$<br><br>$\Rightarrow {(32)^{{{\tan }^2}x}} = {{81} \over {33}}$ <br/><br/>taking log of base 32 both side, <br/><br/>$\Rightarrow$ tan<sup>2</sup>x = ${\log _{32}}\left( {{{81} \over {33}}} \right)$ <br/><br/>$\Rightarrow$ tan x = $\sqrt {{{\log }_{32}}\left( {{{81} \over {33}}} \right)}$ <br/><br/>As value of $\sqrt {{{\log }_{32}}\left( {{{81} \over {33}}} \right)}$ belongs to (0, 1). <br><br>In interval $\,0 \le x \le {\pi \over 4}$ only one solution.

About this question

Subject: Mathematics · Chapter: Trigonometric Functions · Topic: Trigonometric Ratios and Identities

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