Mathematics
Functions
Easy

Question

text  If the function  end text f colon R minus left curly bracket 1 comma negative 1 right curly bracket not stretchy rightwards arrow A text  defined by  end text f left parenthesis x right parenthesis equals fraction numerator x squared over denominator 1 minus x squared end fraction comma text end textis surjective then A =

  1. R minus left square bracket negative 1 comma 0 right parenthesis
  2. R minus left parenthesis negative 1 comma 0 right parenthesis
  3. R minus left curly bracket negative 1 right curly bracket
  4. left square bracket 0 comma straight infinity right parenthesis

The correct answer is: R minus left square bracket negative 1 comma 0 right parenthesis


    text  Let  end text y equals fraction numerator x squared over denominator 1 minus x squared end fraction. text  Then  end text y minus y x squared equals x squared not stretchy rightwards double arrow left parenthesis y plus 1 right parenthesis x squared minus y equals 0
x element of R not stretchy rightwards double arrow text  Discriminant  end text greater or equal than 0 not stretchy rightwards double arrow negative 4 left parenthesis y plus 1 right parenthesis left parenthesis negative y right parenthesis greater or equal than 0 not stretchy rightwards double arrow left parenthesis y plus 1 right parenthesis y greater or equal than 0 not stretchy rightwards double arrow y less or equal than negative 1 text  or  end text y greater or equal than 0
text  If  end text y equals negative 1 text  then  end text fraction numerator x squared over denominator 1 minus x squared end fraction equals negative 1 not stretchy rightwards double arrow x squared equals negative 1 plus x squared text  which is not true.  end text
therefore y less than negative 1 text  or  end text y greater or equal than 0 not stretchy rightwards double arrow text  Range of  end text y text  is  end text R minus left square bracket negative 1 comma 0 right square bracket

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