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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