S n = k = 0 ∑ n ( k n ) ω k . If n is a positive integer and ω = 1 is a cube root of unity, find the number of possible values of the expression above.
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S n = k = 0 ∑ n ( k n ) ω k = ( 1 + ω ) n = ( − ω 2 ) n ( ∵ 1 + ω + ω 2 = 0 )
check the cases ans will be 6 .
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Note that ω + 1 = e ± i π / 3 , a primitive sixth root of unity. Thus S n = ( ω + 1 ) n can attain 6 values, namely, all sixth roots of unity.