Let α and β be the roots of the equation x 2 + x + 1 = 0 , find α 1 0 2 7 + β 1 0 2 7 .
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How exactly do you know α 3 = β 3 ? I understand the rest of the solution
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He showed that if x 2 + x + 1 = 0 ,then x 3 = 1 .Therefore,since α and β satisfy x 2 + x + 1 = 0 ,hence α 3 = β 3 = 1 .
We note that α 2 + α + 1 = 0 ⟹ α 3 = 1 . Similarly for β .
Question, 3 − 1 is imaginary right, not real ?
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( − 1 ) 3 = − 1 ⟹ 3 ( − 1 ) 3 = 3 − 1 ⟹ − 1 = 3 − 1
why is this level 5 ? is it that hard ?
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idk myself, i think some level 4 up get confused
Because of Vieta- Cardano formula α + β = − 1 , α ⋅ β = 1 ⇒ α = β 1 ⇒ α 1 0 2 7 + β 1 0 2 7 = β 1 0 2 7 1 + β 1 0 2 7 = β 1 0 2 7 1 + β 2 0 5 4 , ( 1 ) Due to β 1 0 2 5 ⋅ ( β 2 + β + 1 ) = 0 ⇒ β 1 0 2 7 = − β 1 0 2 6 − β 1 0 2 5 = β 1 0 2 4 , keeping on with this process we get β 1 0 2 7 = β and β 2 0 5 4 = β 2 . Therefore, ( 1 ) = β 1 0 2 7 1 + β 2 0 5 4 = β 1 + β 2 = β − β = − 1
Note.- β = 0
Note first that x 2 + x + 1 = x − 1 x 3 − 1 for x = 1 . Then since 1 is not a solution to x 2 + x + 1 = 0 we know that the roots α , β of this quadratic are such that α 3 = 1 = β 3 .
Then since 1 0 2 7 = 3 ∗ 3 4 2 + 1 we have that α 1 0 2 7 = α and β 1 0 2 7 = β , and so by Vieta's
α 1 0 2 7 + β 1 0 2 7 = α + β = − 1 .
Roots are omega and omega square
Alpha = w and beta = w^2 ... Cube roots of unity
a = (-1 + i sqrt(3))/2 = exp(i 2/3 pi)
b = (-1 - i sqrt(3))/2 = exp(-i 2/3 pi)
2q = a^1027 + b^1027
q = cos(1027*2/3 pi) = -0,5
solution = 2q = -1
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Relevant wiki: Vieta's Formula - Forming Quadratics
x 2 + x + 1 x 3 + x 2 + x x 3 + x 2 + x + 1 x 3 + 0 ⟹ x 3 = 0 = 0 = 1 = 1 = 1 Multiply both sides by x Add both sides by 1
Since α and β are roots of x 2 + x + 1 = 0 , ⟹ α 3 = β 3 = 1 . Therefore,
α 1 0 2 7 + β 1 0 2 7 = α 3 4 2 × 3 + 1 + β 3 4 2 × 3 + 1 = α + β = − 1 By Vieta’s formula