Question:medium

If $\omega$ is a complex cube root of unity, then $(1 - \omega + \omega^2)^5 + (1 + \omega - \omega^2)^5 =$

Show Hint

Always look to substitute $1 + \omega = -\omega^2$ and $1 + \omega^2 = -\omega$ when working with powers of complex cube roots of unity.
Updated On: Jun 3, 2026
  • $32$
  • $-32$
  • $64$
  • $-64$
Show Solution

The Correct Option is A

Solution and Explanation

Step 1: Recall the omega facts.
A complex cube root of unity $\omega$ has two key properties: $1 + \omega + \omega^2 = 0$ and $\omega^3 = 1$. From the first, $1 + \omega^2 = -\omega$ and $1 + \omega = -\omega^2$.

Step 2: Simplify the first bracket.
Take $1 - \omega + \omega^2$. Group as $(1 + \omega^2) - \omega = -\omega - \omega = -2\omega$.

Step 3: Raise it to the 5th power.
Compute $(-2\omega)^5 = -32\omega^5$. Since $\omega^5 = \omega^3\cdot\omega^2 = \omega^2$, this is $-32\omega^2$.

Step 4: Simplify the second bracket.
Take $1 + \omega - \omega^2$. Group as $(1 + \omega) - \omega^2 = -\omega^2 - \omega^2 = -2\omega^2$.

Step 5: Raise it to the 5th power.
Compute $(-2\omega^2)^5 = -32\omega^{10}$. Since $\omega^{10} = (\omega^3)^3\cdot\omega = \omega$, this is $-32\omega$.

Step 6: Add the two results.
Sum them: $-32\omega^2 - 32\omega = -32(\omega + \omega^2)$. Since $\omega + \omega^2 = -1$, this is $-32(-1) = 32$.
\[ \boxed{32} \]
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