sin 1 4 π sin 1 4 3 π sin 1 4 5 π sin 1 4 7 π sin 1 4 9 π sin 1 4 1 1 π sin 1 4 1 3 π = 2 n
Find n .
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How sin x =cos(π\2-x)
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Please read up this link . Also read up our wiki on Trigonometry .
Very nice approach
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sin 1 4 π sin 1 4 3 π sin 1 4 5 π sin 1 4 7 π sin 1 4 9 π sin 1 4 1 1 π sin 1 4 1 3 π As sin x = cos ( 2 π − x ) and cos ( − x ) = cos x = cos 1 4 6 π cos 1 4 4 π cos 1 4 2 π cos 0 cos 1 4 2 π cos 1 4 4 π cos 1 4 6 π = ( cos 7 π cos 7 2 π cos 7 3 π ) 2 As cos x = − cos ( π − x ) = ( − cos 7 π cos 7 2 π cos 7 4 π ) 2 = ( − sin 7 π sin 7 π cos 7 π cos 7 2 π cos 7 4 π ) 2 = ( − 2 sin 7 π sin 7 2 π cos 7 2 π cos 7 4 π ) 2 = ( − 4 sin 7 π sin 7 4 π cos 7 4 π ) 2 = ( − 8 sin 7 π sin 7 8 π ) 2 As cos x = − cos ( π − x ) = ( 8 sin 7 π sin 7 π ) 2 = ( 8 1 ) 2 = 2 6 1
⟹ n = − 6