Mathematics
Functions
Easy

Question

The function f(x) is defined for all real x. If f(a+b) =f(ab) for all a text  and  end text b text  and  end text f open parentheses negative 1 half close parentheses equals negative 1 half then find the value of f(1005)

  1. negative 1 divided by 2
  2. negative 3 divided by 2
  3. negative 5 divided by 2
  4. negative 7 divided by 2

The correct answer is: negative 1 divided by 2


    text  We have  end text f left parenthesis a plus b right parenthesis equals f left parenthesis a b right parenthesis straight for all a text  and  end text b
text  Put  end text space of 1em a equals 0
therefore space of 1em f left parenthesis b right parenthesis equals f left parenthesis 0 right parenthesis equals k left parenthesis text  say  end text right parenthesis
text  Putting  end text b equals 0 text  in given relation,  end text
f left parenthesis a right parenthesis equals f left parenthesis 0 right parenthesis equals k
text  Thus  end text f left parenthesis a right parenthesis equals f left parenthesis b right parenthesis equals k straight for all a comma b
text  Hence,  end text f left parenthesis x right parenthesis text  is a constant function.  end text
table attributes columnalign right left right left right left right left right left right left columnspacing 0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em rowspacing 3 pt end attributes row cell therefore space of 1em f left parenthesis 1005 right parenthesis equals f open parentheses negative 1 half close parentheses end cell row cell equals negative 1 half end cell end table

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