If $\alpha , \beta $ are the roots of the equation $x^2 - 2x + 4 = 0$ , then the value of $\alpha ^n +\beta ^n$ is

  • A

    ${2^n}\cos \left( {\frac{{n\pi }}{3}} \right)$

  • B

    ${2^{n + 1}}\cos \left( {\frac{{n\pi }}{3}} \right)$

  • C

    ${2^n}\sin \left( {\frac{{n\pi }}{3}} \right)$

  • D

    ${2^{n + 1}}\sin \left( {\frac{{n\pi }}{3}} \right)$

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