If $x,y,z$  are in $A.P.$ and  ${\tan ^{ - 1}}x,{\tan ^{ - 1}}y$ and ${\tan ^{ - 1}}z$ are also in other $A.P.$ then  . . . 

  • [JEE MAIN 2013]
  • A

    $x = y = z$

  • B

    $x = y = - z$

  • C

    $x = 1;y = 2;z = 3$

  • D

    $x = 2;y = 4;z = 6$

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