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Let omega be a cube root of unity not eq...

Let `omega` be a cube root of unity not equal to 1. Then the maximum possible value of `| a + bw + cw^(2) |` where a, b, c `in` {+1, -1} is

A

0

B

2

C

`sqrt(3) `

D

`1 + sqrt(3)`

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The correct Answer is:
To solve the problem, we need to find the maximum possible value of the expression \( | a + b\omega + c\omega^2 | \), where \( a, b, c \in \{+1, -1\} \) and \( \omega \) is a cube root of unity not equal to 1. ### Step-by-Step Solution: 1. **Understanding Cube Roots of Unity:** The cube roots of unity are the solutions to the equation \( x^3 = 1 \). The roots are \( 1, \omega, \omega^2 \), where: \[ \omega = e^{2\pi i / 3} = -\frac{1}{2} + i\frac{\sqrt{3}}{2} \] \[ \omega^2 = e^{-2\pi i / 3} = -\frac{1}{2} - i\frac{\sqrt{3}}{2} \] 2. **Expressing the Given Expression:** We need to evaluate: \[ | a + b\omega + c\omega^2 | \] where \( a, b, c \) can be either \( +1 \) or \( -1 \). 3. **Substituting Values:** We will consider all combinations of \( a, b, c \). The possible combinations of \( (a, b, c) \) are \( (+1, +1, +1), (+1, +1, -1), (+1, -1, +1), (+1, -1, -1), (-1, +1, +1), (-1, +1, -1), (-1, -1, +1), (-1, -1, -1) \). 4. **Calculating Each Case:** Let's compute the modulus for each case: - For \( (1, 1, 1) \): \[ |1 + \omega + \omega^2| = |1 + (-\frac{1}{2} + i\frac{\sqrt{3}}{2}) + (-\frac{1}{2} - i\frac{\sqrt{3}}{2})| = |1 - 1| = 0 \] - For \( (1, 1, -1) \): \[ |1 + \omega - \omega^2| = |1 + (-\frac{1}{2} + i\frac{\sqrt{3}}{2}) - (-\frac{1}{2} - i\frac{\sqrt{3}}{2})| = |1 + i\sqrt{3}| = 2 \] - For \( (1, -1, 1) \): \[ |1 - \omega + \omega^2| = |1 - (-\frac{1}{2} + i\frac{\sqrt{3}}{2}) + (-\frac{1}{2} - i\frac{\sqrt{3}}{2})| = |1 + 1| = 2 \] - For \( (1, -1, -1) \): \[ |1 - \omega - \omega^2| = |1 - (-\frac{1}{2} + i\frac{\sqrt{3}}{2}) - (-\frac{1}{2} - i\frac{\sqrt{3}}{2})| = |1| = 1 \] - For \( (-1, 1, 1) \): \[ |-1 + \omega + \omega^2| = |-1 + 0| = 1 \] - For \( (-1, 1, -1) \): \[ |-1 + \omega - \omega^2| = |-1 + i\sqrt{3}| = 2 \] - For \( (-1, -1, 1) \): \[ |-1 - \omega + \omega^2| = |-1 + 0| = 1 \] - For \( (-1, -1, -1) \): \[ |-1 - \omega - \omega^2| = |-1| = 1 \] 5. **Finding the Maximum Value:** The maximum value from all computed cases is \( 2 \). ### Conclusion: The maximum possible value of \( | a + b\omega + c\omega^2 | \) is \( \boxed{2} \).
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