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We have to verify sin 25 + sin 35 = cos 5

sin 25 + sin 35

=> 2* sin (25 + 35)/2 * cos 10/2

=> 2* sin (60)/2 * cos 5

=> 2* sin 30 * cos 5

sin 30 = 1/2

=> 2 * (1/2) cos 5

=> cos 5

This proves that sin 25 + sin 35 = cos 5

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