sin 1 4 π ⋅ sin 1 4 3 π ⋅ sin 1 4 5 π = ?
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Very clever manipulation, nicely done
Nice variant of Morrie's Law
Using cos ( x ) = sin ( π / 2 − x ) and ∏ k = 0 n − 1 cos ( 2 k x ) = 2 n sin ( x ) sin ( 2 n x ) we can write the given expression as − cos ( 8 π / 1 4 ) cos ( 4 π / 1 4 ) cos ( 2 π / 1 4 ) = − 2 3 sin ( 2 π / 1 4 ) sin ( 1 6 π / 1 4 ) = 0 . 1 2 5
cos ( x ) = sin ( x − 2 π )
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oops...typo.. the New Year's festivities are getting me confused
lol.. it's a simple problem just type it in the calculator! Why make the simple complicated. lol. peace man
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But you won't have calculator during exam..
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Here in the philippines our exams are using the aid of a calculator.. stupid isn't it? We're trained to be idiots and not intellectuals
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@Okay Fine – Filipino here! and what did you say ? idiots? Shame on you, I know you are a filipino too!
@Okay Fine – I wish i lived in philippines.........
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Here I shall provide a relatively elementary approach (in comparison to @Otto Bretscher 's!):
sin 1 4 π ⋅ sin 1 4 3 π ⋅ sin 1 4 5 π = cos 1 4 6 π ⋅ cos 1 4 4 π ⋅ cos 1 4 2 π = cos 7 π ⋅ cos 7 2 π ⋅ cos 7 3 π = − cos 7 π ⋅ cos 7 2 π ⋅ cos 7 4 π = sin 7 π − sin 7 π ⋅ cos 7 π ⋅ cos 7 2 π ⋅ cos 7 4 π = 2 sin 7 π − sin 7 2 π ⋅ cos 7 2 π ⋅ cos 7 4 π = 4 sin 7 π − sin 7 4 π ⋅ cos 7 4 π = 8 sin 7 π − sin 7 8 π = 8 1 ⋅ sin 7 π sin 7 π = 0 . 1 2 5 .