Saurabh Koranglekar
Last Activity: 5 Years ago
S =sin x + sin 3x +sin 5x +sin7x+.....+sin 29x
(2.sin x). S = (2.sin x). (sin x + sin 3x +sin 5x +sin7x+.....+sin 29x)
(2.sin x). S = 2.sin x.sen x +2. without 3x.sin x + 2.sin 5x.sin x + 2.sin7x.sin x + ..... + 2.sin 29x.sin x
2.sinA.sinB = cos (A-B) -cos (A+B), similarly
2.sin x.sin x = cos (x-x) -cos (x + x) = cos (0) -cos (2x) = 1-cos (2x)
2. sin 3x.sin x = cos (3x-x) -cos (3x + x) = cos (2x) -cos (4x)
2.sin 5x.sin x = cos (5x-x) -cos (5x + x) = cos (4x) -cos (6x)
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2.sin 29x.sin x = cos (29x-x) -cos (29x + x) = cos (28x) -cos (30x)
S = 1-cos (2x) + cos (2x) -cos (4x) + cos (4x) -cos (6x) + ... + cos(28x) -cos (30x)
(2.sin x) .S = 1-cos (30x)
(2.sin x) .S = 1- [cos² (15x) -sin (15x)]
(2.sin x) .S = 1-cos² (15x) + sin² (15x)
(2.sin x) .S = sin² (15x) + sin² (15x)
(2.sin x). S = 2.sin² (15x)
S = sin² (15x) / sin (x)