Medium MCQ +4 / -1 PYQ · JEE Mains 2020

Let $\alpha$ and $\beta$ be two real roots of the equation
(k + 1)tan2x - $\sqrt 2$ . $\lambda$tanx = (1 - k), where k($\ne$ - 1) and $\lambda$ are real numbers. if tan2 ($\alpha$ + $\beta$) = 50, then a value of $\lambda$ is:

  1. A 5$\sqrt 2$
  2. B 10 Correct answer
  3. C 5
  4. D 10$\sqrt 2$

Solution

Let tan$\alpha$ and tan$\beta$ are the roots of <br><br>(k + 1)tan<sup>2</sup>x - $\sqrt 2$ . $\lambda$tanx - (1 - k) = 0 <br><br>$\therefore$ tan$\alpha$ + tan$\beta$ = ${{\sqrt 2 \lambda } \over {k + 1}}$ <br><br>and an$\alpha$.tan$\beta$ = ${{k - 1} \over {k + 1}}$ <br><br>Now tan($\alpha$ + $\beta$) <br><br>= ${{\tan \alpha + \tan \beta } \over {1 - \tan \alpha \tan \beta }}$ <br><br>= ${{{{\lambda \sqrt 2 } \over {k + 1}}} \over {1 - {{k - 1} \over {k + 1}}}}$ <br><br>= ${{{\lambda \sqrt 2 } \over 2}}$ = ${{\lambda \over {\sqrt 2 }}}$ <br><br>Given ${{{{\lambda ^2}} \over 2}}$ = 50 <br><br>$\Rightarrow$ $\lambda$ = 10

About this question

Subject: Mathematics · Chapter: Complex Numbers and Quadratic Equations · Topic: Complex Numbers and Argand Plane

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