# If Tan ( π / 4 + X ) + Tan ( π / 4 − X ) = λ Sec 2 X , Then - Mathematics

MCQ

If $\tan \left( \pi/4 + x \right) + \tan \left( \pi/4 - x \right) = \lambda \sec 2x, \text{ then }$

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#### Solution

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$\text{ Given } :$

$\tan\left( \frac{\pi}{4} + x \right) + \tan\left( \frac{\pi}{4} - x \right) = \lambda \sec 2x$

$\Rightarrow \frac{\tan\frac{\pi}{4} + \text{ tan } x}{1 - \tan\frac{\pi}{4} \times \text{ tan } x} + \frac{\tan\frac{\pi}{4} - \text{ tan } x}{1 + \tan\frac{\pi}{4} \times \text{ tan } x} = \lambda \sec 2x$

$\Rightarrow \frac{1 + \text{ tan } x}{1 - \text{ tan } x} + \frac{1 - \text{ tan } x}{1 + \text{ tan } x} = \lambda \sec 2x$

$\Rightarrow \frac{\left( 1 + \text{ tan } x \right)^2 + \left( 1 - \text{ tan } x \right)^2}{\left( 1 - \text{ tan } x \right)\left( 1 + \text{ tan } x \right)} = \lambda \sec 2x$

$\Rightarrow \frac{2\left( 1 + \tan^2 x \right)}{1 - \tan^2 x} = \lambda \sec 2x$

$\Rightarrow \frac{2 \sec^2 x}{1 - \tan^2 x} = \lambda \sec 2x$

$\Rightarrow \frac{2}{\cos^2 x\left( 1 - \tan^2 x \right)} = \lambda \sec 2x$

$\Rightarrow \frac{2}{\cos^2 x\left( 1 - \frac{\sin^2 x}{\cos^2 x} \right)} = \lambda \sec 2x$

$\Rightarrow \frac{2}{\cos^2 x - \sin^2 x} = \lambda \sec 2x$

$\Rightarrow \frac{2}{\cos2x} = \lambda \sec 2x$

$\Rightarrow 2\sec2x = \lambda \sec 2x$

$\Rightarrow 2 = \lambda$

$\therefore \lambda = 2$

Concept: Values of Trigonometric Functions at Multiples and Submultiples of an Angle
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#### APPEARS IN

RD Sharma Class 11 Mathematics Textbook
Chapter 9 Values of Trigonometric function at multiples and submultiples of an angle
Q 19 | Page 44