Mathematics
Functions
Easy

Question

Let f(x) be a function and k be a positive real number such that

f left parenthesis x plus k right parenthesis plus f left parenthesis x right parenthesis equals 0 space f o r space a l l space x element of R. space t h e n space f i n d space t h e space p e r i o d space o f space f left parenthesis x right parenthesis space

  1. 2 k
  2. 3 k
  3. 4 k
  4. 5 k

The correct answer is: 2 k


    text  We have  end text f left parenthesis x plus k right parenthesis plus f left parenthesis x right parenthesis equals 0 straight for all x element of R
o r space space f left parenthesis x plus k right parenthesis equals negative f left parenthesis x right parenthesis straight for all x element of R
text  Put  end text x equals x plus k. text  Then,  end text
o r space space f left parenthesis x plus 2 k right parenthesis equals negative f left parenthesis x plus k right parenthesis straight for all x element of R
o r space space f left parenthesis x plus 2 k right parenthesis equals f left parenthesis x right parenthesis comma straight for all x element of R space space space space space space space space left square bracket text  As  end text f left parenthesis x plus k right parenthesis equals negative f left parenthesis x right parenthesis right square bracket
text  which clearly shows that  end text f left parenthesis x right parenthesis text  is periodic with period  end text 2 k text  .  end text

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