MCQ
The maximum value of the expression $E = sin \theta + cos \theta + sin2 \theta$ is-
  • A
    $\tan \frac{\pi }{4}$
  • B
    $\tan \frac{\pi }{3}$
  • C
    $\tan \frac{\pi }{8}$
  • $\tan \frac{3\pi }{8}$

Answer

Correct option: D.
$\tan \frac{3\pi }{8}$
d
$E=\sin \theta+\cos \theta+2 \sin \theta \cos \theta$

Let $t=\sin \theta+\cos \theta$

$-\sqrt{2} \leq t \leq \sqrt{2}$

$E=t+t^{2}-1$

$=\left(t+\frac{1}{2}\right)^{2}-\frac{5}{4} $

$\Rightarrow E_{\max }=\left(\sqrt{2}+\frac{1}{2}\right)^{2}-\frac{5}{4}$

$=1+\sqrt{2}=\tan \frac{3 \pi}{8}$

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