Trigonometrical Equations
normal

 $x  \in \left[ { - \frac{\pi }{4},\frac{\pi }{4}} \right]$ માં $x$ ની કેટલી કિમત મળે કે જેથી $2sin^22x = 2cos^28x + cos10x$ થાય 

A

$10$

B

$12$

C

$14$

D

$16$

Solution

$cos16x + cos10x + cos4x = 0$ $cos10x + 2 cos10x cos6x = 0$ $cos10x = 0$ or $cos6x =-\frac{1}{2}$ $x = (2n-1)\frac{\pi }{20}$ or $x = \frac{n\pi }{3} \pm \frac{\pi }{9},n \in I$ $\therefore$ Total number of values $= 10$

Standard 11
Mathematics

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