Let $\vec A\, = \,(\hat i\, + \,\hat j)\,$  and $\vec B\, = \,(2\hat i\, - \,\hat j)\,.$  The magnitude of a coplanar vector $\vec C$ such that  $\vec A\cdot \vec C\, = \,\vec B\cdot \vec C\, = \vec A\cdot \vec B$ is given by

  • [JEE MAIN 2018]
  • A

    $\sqrt {\frac{5}{9}} $

  • B

    $\sqrt {\frac{10}{9}} $

  • C

    $\sqrt {\frac{20}{9}} $

  • D

    $\sqrt {\frac{9}{12}} $

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