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$I f 0 \leq x < 2 π, t h e n t h e n u m b e r o f r e a l v a l u e s o f x, w h i c h s a t i s f y t h e e q u a t i o n \cos x + \cos 2 x + \cos 3 x + \cos 4 x = 0, i s$

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Correct option is B

cos4x+cosx+cos3x+cos2x=0 ⇒2cos5x2cos3x2+2cos5x2cosx2=0 by transformations ⇒cos5x2cos3x2+cosx2=0 ⇒cos5x22cosx cosx2=0 ⇒∴x=π5,π2,3π5,π,7π5,3π2,9π5

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If 0≤x<2π, then the number of real values of x, which satisfy the equation cosx+cos2x+cos3x+cos4x=0 , is

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$I f 0 \leq x < 2 π, t h e n t h e n u m b e r o f r e a l v a l u e s o f x, w h i c h s a t i s f y t h e e q u a t i o n \cos x + \cos 2 x + \cos 3 x + \cos 4 x = 0, i s$