Problem

Problem

If 0≤x<2π0 \le x < 2\pi , then the number of real values of xx , which satisfy the equation cos⁡x+cos⁡2x+cos⁡3x+cos⁡4x=0\cos x + \cos 2x + \cos 3x + \cos 4x = 0 , is a. 3 b. 5 c. 7 d. 9

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