Maths-
General
Easy

Question

If f colon R rightwards arrow R be a positive increasing function with L t left parenthesis x rightwards arrow infinity right parenthesis space space left parenthesis f left parenthesis 3 x right parenthesis right parenthesis divided by left parenthesis f left parenthesis x right parenthesis right parenthesis equals 1 spacethen L t left parenthesis x rightwards arrow infinity right parenthesis space space left parenthesis f left parenthesis 2 x right parenthesis right parenthesis divided by left parenthesis f left parenthesis x right parenthesis right parenthesis

  1. 1
  2. 2 divided by 3
  3. space 3 divided by 2
  4. 3

hintHint:

In this question we are given  f left parenthesis x right parenthesis is an increasing for all x greater than 0. Then we will use sandwich theorem to find the value of the limit

The correct answer is: 1


    In this question we are givenlimit as x rightwards arrow infinity of equals fraction numerator f left parenthesis 3 x right parenthesis over denominator f left parenthesis x right parenthesis end fraction equals 1 and we have to find the value of limit as x rightwards arrow infinity of fraction numerator f left parenthesis 2 x right parenthesis over denominator f left parenthesis x right parenthesis end fraction
    Step1: Using Sandwich Theorem
    In the question we are given f left parenthesis x right parenthesis is an increasing for all x greater than 0. Then
    f left parenthesis x right parenthesis less or equal than f left parenthesis 2 x right parenthesis less or equal than f left parenthesis 3 x right parenthesis
    By dividing by f left parenthesis x right parenthesis we get,
    => fraction numerator f left parenthesis x right parenthesis over denominator f left parenthesis x right parenthesis end fraction less or equal than fraction numerator f left parenthesis 2 x right parenthesis over denominator f left parenthesis x right parenthesis end fraction less or equal than fraction numerator f left parenthesis 3 x right parenthesis over denominator f left parenthesis x right parenthesis end fraction
    By taking the limit limit as x rightwards arrow infinity of we get
    => limit as x rightwards arrow infinity of fraction numerator f left parenthesis x right parenthesis over denominator f left parenthesis x right parenthesis end fraction less or equal than limit as x rightwards arrow infinity of fraction numerator f left parenthesis 2 x right parenthesis over denominator f left parenthesis x right parenthesis end fraction less or equal than limit as x rightwards arrow infinity of fraction numerator f left parenthesis 3 x right parenthesis over denominator f left parenthesis x right parenthesis end fraction
    Given limit as x rightwards arrow infinity of equals fraction numerator f left parenthesis 3 x right parenthesis over denominator f left parenthesis x right parenthesis end fraction equals 1 and we can see that limit as x rightwards arrow infinity of equals fraction numerator f left parenthesis x right parenthesis over denominator f left parenthesis x right parenthesis end fraction equals 1
    =>1 less or equal than limit as x rightwards arrow infinity of fraction numerator f left parenthesis 2 x right parenthesis over denominator f left parenthesis x right parenthesis end fraction less or equal than 1
    So, the value of the limit as x rightwards arrow infinity of fraction numerator f left parenthesis 2 x right parenthesis over denominator f left parenthesis x right parenthesis end fraction is 1

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