The maximum value of

Question:

The maximum value of $3 \cos \theta+5 \sin \left(\theta-\frac{\pi}{6}\right)$ for any real value of $\theta$ is :

  1. $\sqrt{19}$

  2. $\frac{\sqrt{79}}{2}$

  3. $\sqrt{31}$

  4. $\sqrt{34}$


Correct Option: 1

Solution:

$y=3 \cos \theta+5\left(\sin \theta \frac{\sqrt{3}}{2}-\cos \theta \frac{1}{2}\right)$

$\frac{5 \sqrt{3}}{2} \sin \theta+\frac{1}{2} \cos \theta$

$\mathrm{y}_{\max }=\sqrt{\frac{75}{4}+\frac{1}{4}}=\sqrt{19}$

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