If a , b , c are distinct roots of the equation x 3 − 1 = 0 , find the value of a 1 7 2 9 + b 1 7 2 9 + c 1 7 2 9 .
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Good approach making use of x 3 = 1 .
Did it the same way... #cuberootofunityrocks :>
If you don't have an idea of cube roots of unity, here's an alternate approach. x 3 = 1 ⟹ ( x 3 ) 5 7 6 = 1 5 7 6 = 1 ⟹ x 1 7 2 8 = 1 ⟹ x 1 7 2 9 = x ⟹ a 1 7 2 9 = a , b 1 7 2 9 = b , c 1 7 2 9 = c ∴ a 1 7 2 9 + b 1 7 2 9 + c 1 7 2 9 = a + b + c = 0 Since sum of roots of x 3 − 1 = 0 is 1 0 = 0 .
a 1 7 2 9 + b 1 7 2 9 + c 1 7 2 9 = a 1 7 2 8 ⋅ a + b 1 7 2 8 ⋅ b + c 1 7 2 8 ⋅ c ( a 3 ) 5 7 6 ⋅ a + ( b 3 ) 5 7 6 ⋅ b + ( c 3 ) 5 7 6 ⋅ c = a + b + c Using Vieta's Formula we have a + b + c = 0
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Note that ( a , b , c ) = ( 1 , ω , ω 2 ) where ω is complex cube root of unity. Hence ,
a 1 7 2 9 + b 1 7 2 9 + c 1 7 2 9 = 1 1 7 2 9 + ω 1 7 2 9 + ω 3 4 5 8
Now using ω 3 = 1 , we have:
1 1 7 2 9 + ω 1 7 2 9 + ω 3 4 5 8 = 1 + ω + ω 2 = 0