For a suitably chosen real constant $a$, let a function, $f: R-\{-a\} \rightarrow R$ be defined by $f(x)=\frac{a-x}{a+x} .$ Further suppose that for any real number $x \neq- a$ and $f( x ) \neq- a ,( fof )( x )= x .$ Then $f\left(-\frac{1}{2}\right)$ is equal to

  • [JEE MAIN 2020]
  • A

    $\frac{1}{3}$

  • B

    $3$

  • C

    $-3$

  • D

    $-\frac{1}{3}$

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