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Question: Answered & Verified by Expert
If $\alpha$ and $\beta$ are the roots of $x^{2}-x+1=0,$ then the equation whose roots are $\alpha^{100}$ and $\beta^{100}$ are
MathematicsComplex NumberBITSATBITSAT 2013
Options:
  • A $x^{2}-x+1=0$
  • B $x^{2}+x-1=0$
  • C $x^{2}-x-1=0$
  • D $x^{2}+x+1=0$
Solution:
2599 Upvotes Verified Answer
The correct answer is: $x^{2}+x+1=0$
We have $x^{3}+1 \equiv(x+1)\left(x^{2}-x+1\right)$. Therefore, $\alpha$ and $\beta$ are the complex cube roots of -1 so that we may take $\alpha=-\omega$ and $\beta=-\omega^{2},$ where $\omega \neq 1$ is a cube root of unity.

Thus $\alpha^{100}=(-\omega)^{100}=\omega$ and

$\beta^{100}=\left(-\omega^{2}\right)^{100}=\omega^{2},$ so that the required

equation is $\mathrm{x}^{2}+\mathrm{x}+1=0$

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