1.

Find the general solution of the equation sinx – 3sin2x + sin3x = cosx – 3cos2x + cos3x

Answer»

We have, (sin x + sin 3x) – 3 sin 2x = (cos x + cos 3x) – 3 cos 2x

=> 2 sin 2x cos x – 3 sin 2x = 2 cos 2x.cos x – 3 cos 2x

=> sin 2x(2 cos x – 3) = cos 2x(2 cos x – 3)

=> sin 2x = cos 2x (As cos x ≠ 3/2)

=> tan 2x = 1 => tan 2x = tan π/4

=> 2x = nπ + π/4 , n∈Z

x = nπ/2 +π/8 , n∈Z



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