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Not required since the expression is simply:
1 6 { e 4 i π / 3 + e − 4 i π / 3 } = 3 2 ℜ ( e 4 i π / 3 ) = 3 2 ⋅ cos 3 4 π
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Just wanted to show it can be solved using simple algebra.
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Ohk... Great.. (+1)....
Just a genuine query: Where has that option of 'Unsubscribe from comments' gone, previously it used to be in the bottom right corner of our solutions ?
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@Rishabh Jain – Don't know, I have never used it but I saw it there.
( − 1 + − 3 ) 4 + ( − 1 − − 3 ) 4 = ( 2 . 2 ( − 1 + − 3 ) ) 4 + ( 2 . 2 ( − 1 − − 3 ) ) 4 = 2 4 . ω 4 + 2 4 . ( ω 2 ) 4 = 2 4 ( ω + ω 2 ) = 1 6 × ( − 1 ) = − 1 6
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Let a = − 1 and b = − 3 . Then we have:
( a + b ) 4 + ( a − b ) 4 = a 4 + 4 a 3 b + 6 a 2 b 2 + 4 a b 3 + b 4 + a 4 − 4 a 3 b + 6 a 2 b 2 − 4 a b 3 + b 4 = 2 ( a 4 + 6 a 2 b 2 + b 4 ) = 2 ( ( − 1 ) 4 + 6 ( − 1 ) 2 ( − 3 ) 2 + ( − 3 ) 4 ) = 2 ( 1 + 6 ( − 3 ) + 9 ) = − 1 6
Alternative Solution
( − 1 + − 3 ) 4 + ( − 1 − − 3 ) 4 = ( − 1 + i 3 ) 4 + ( − 1 − i 3 ) 4 = 2 4 ( − 2 1 + i 2 3 ) 4 + 2 4 ( − 2 1 − i 2 3 ) 4 = 1 6 ( cos 3 2 π + i sin 3 2 π ) 4 + 1 6 ( cos 3 − 2 π + i sin 3 − 2 π ) 4 = 1 6 ( e i 3 2 π ) 4 + 1 6 ( e − i 3 2 π ) 4 = 1 6 e i 3 8 π + 1 6 e − i 3 8 π = 1 6 ( cos 3 8 π + i sin 3 8 π ) + 1 6 ( cos 3 − 8 π + i sin 3 − 8 π ) = 1 6 ( cos 3 8 π + i sin 3 8 π ) + 1 6 ( cos 3 8 π − i sin 3 8 π ) = 3 2 cos 3 8 π = − 1 6