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Question

Consider the following statements in respect of the function $f(x) = x$ in the interval (-1, 1) :
I. The function attains maximum value.
II. The function attains minimum value.
Which of the statements given above is/are correct ?

The correct answer is
Neither I nor II

Function Analysis: $f(x) = x$

The function given is $f(x) = x$. This is a simple linear function that increases as $x$ increases.

Interval Consideration: Open Interval $(-1, 1)$

The interval specified is $(-1, 1)$. This is an open interval, meaning it includes all numbers between -1 and 1, but not -1 and 1 themselves. Mathematically, $x \in (-1, 1)$ means $-1 < x < 1$.

Statement I: Maximum Value Attainment

In the interval $(-1, 1)$, the values of $f(x) = x$ range strictly between -1 and 1.

  • As $x$ gets closer and closer to 1 (e.g., 0.9, 0.99, 0.999), $f(x)$ gets closer to 1.
  • However, since $x$ must be less than 1, $f(x)$ can never be exactly equal to 1.
  • Therefore, the function does not attain a maximum value within the open interval $(-1, 1)$. The supremum is 1, but it is not reached.

Statement II: Minimum Value Attainment

Similarly, in the interval $(-1, 1)$:

  • As $x$ gets closer and closer to -1 (e.g., -0.9, -0.99, -0.999), $f(x)$ gets closer to -1.
  • However, since $x$ must be greater than -1, $f(x)$ can never be exactly equal to -1.
  • Therefore, the function does not attain a minimum value within the open interval $(-1, 1)$. The infimum is -1, but it is not reached.

Conclusion

Since neither statement I nor statement II is correct, the correct option is that the function attains neither its maximum nor its minimum value in the given open interval.

Correct Answer: Neither I nor II

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Important Questions from Maxima and Minima

  1. Four small squares of side x are cut out of a square of side 12 cm to make a tray by folding the edges. What is the value of x so that the tray has the maximum volume?

  2. If 3 ≤ x ≤ 10 and 5 ≤ y ≤ 15 , then maximum value of \(\left(\frac{x}{y}\right)\) is-

  3. If N is a four digit number formed by digits x 1, x 2, x 3and x 4, then maximum value of \(\frac{N}{x_{1}+x_{2}+x_{3}+x_{4}}\) is-

  4. A wire of length 20 cm is to be bent into a rectangle. Which of the following statements is/are correct?

    I. The rectangle of the largest area is the square.
    II. It is possible to form a rectangle of an area of $27 \, \text{cm}^2$.

    Select the answer using the code given below.

  5. Consider the following statements :

    Statement-I : 
    The function $f(x) = \frac{x^3 + 128}{x}$ has a minimum value 48 at $x = 4$.

    Statement-II : 
    As $x$ increases through 4, $f'(x)$ changes sign from positive to negative.

    Which one of the following is correct in respect of the above statements?

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