sin 47 + sin 61 - sin11 - sin 25

Asked by  | 1st Sep, 2012, 11:17: AM

Expert Answer:

(sin47 - sin25) + (sin61 - sin11)

(2cos36 x sin11) + (2cos36 x sin25)

2cos36 ( sin11 + sin25)

4cos36 x sin18 x cos7

sin18 = (root5 - 1)/4 and cos36 = (root5 + 1)/4

so on solving we get, cos7.

Answered by  | 2nd Sep, 2012, 11:35: AM

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