Maths-
General
Easy

Question

If f open parentheses x close parentheses equals fraction numerator 1 over denominator x plus 1 end fraction minus log invisible function application left parenthesis 1 plus x right parenthesis comma blank x greater than 0, then f is

  1. an increasing function  
  2. a decreasing function  
  3. both increasing and decreasing function  
  4. None of the above  

The correct answer is: a decreasing function


    Given curve is f open parentheses x close parentheses equals fraction numerator 1 over denominator x plus 1 end fraction minus log invisible function application open parentheses 1 plus x close parentheses
    On differentiating w.r.t. x, we get

    f to the power of ´ end exponent open parentheses x close parentheses equals negative fraction numerator 1 over denominator open parentheses x plus 1 close parentheses to the power of 2 end exponent end fraction minus fraction numerator 1 over denominator 1 plus x end fraction

    rightwards double arrow blank f to the power of ´ end exponent open parentheses x close parentheses equals negative open square brackets fraction numerator 1 over denominator x plus 1 end fraction plus fraction numerator 1 over denominator open parentheses x plus 1 close parentheses to the power of 2 end exponent end fraction close square brackets

    rightwards double arrow blank f to the power of ´ end exponent open parentheses x close parentheses equals negativeve, when x greater than 0

    therefore blank f left parenthesis x right parenthesis is a decreasing function

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