KVPY 2019 SB SX Exam Previous Papers

Question : 9 of 120

Marks: +1, -0

The number of solutions of the equation sin(9x) + sin(3x) = 0 in the closed interval [0, 2π] is

Solution:

\sin 9x + \sin 3x = 0

⇒

2\sin 6x \cos 3x = 0

⇒

4 \sin 3x \cos^2 3x = 0

⇒

\sin 3x = 0 \or \cos 3x = 0

⇒

7 + 6 = 13

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