Trigonometrical Equations
normal

If $sin\, \theta = sin\, \alpha$ then $sin\, \frac{\theta }{3}$ =

A

$sin\, \frac{\alpha }{3}$

B

$sin \, \left( {\frac{\pi }{3} - \frac{\alpha }{3}} \right)$

C

$- sin \, \left( {\frac{\pi }{3} + \frac{\alpha }{3}} \right)$

D

All of the above

Solution

$sin \theta = sin \alpha$ 

          $\theta = n\pi +(-1)^n\alpha$

$n = 0$    $\theta = \alpha$                $sin\theta /3 = sin\alpha /3$

$n = 1$    $\theta = \pi -\alpha$          $sin\theta /3 = sin(\pi /3-\alpha /3)$

$n = -1$    $\theta = -\pi -\alpha$        $sin\theta /3 = sin(-\pi /3-\alpha /3)= -sin(\pi /3+\alpha /3)$

Standard 11
Mathematics

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