Let $f (x) = a^x (a > 0)$ be written as $f( x) = f_1( x) + f_2( x)$ , where $f_1( x)$ is an even function and $f_2( x)$ is an odd function. Then $f_1( x + y) + f_1( x - y )$ equals

  • [JEE MAIN 2019]
  • A

    $2{f_1}\left( x \right){f_2}\left( y \right)$

  • B

    $2{f_1}\left( x \right){f_1}\left( y \right)$

  • C

    $2{f_1}\left( {x + y} \right){f_2}\left( {x - y} \right)$

  • D

    $2{f_1}\left( {x + y} \right){f_1}\left( {x - y} \right)$

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