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Let f(x) be a function defined in 1lexle...

Let f(x) be a function defined in `1lexleoo` by
`f(x)={{:(2-x" for "1lexle2),(3x-x^(2)" for "xgt2):}`
Consider the following statements :
1. f'(2+0) does not exist.
2. f'(2-0) does not exist.
Which of the above statements is/are correct?

A

1 only

B

2 only

C

Both 1 and 2

D

Neither 1 nor 2

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to analyze the function \( f(x) \) defined as follows: \[ f(x) = \begin{cases} 2 - x & \text{for } 1 \leq x \leq 2 \\ 3x - x^2 & \text{for } x > 2 \end{cases} \] We need to check the existence of the derivatives \( f'(2+0) \) and \( f'(2-0) \). ### Step 1: Calculate \( f(2) \) First, we find the value of the function at \( x = 2 \): \[ f(2) = 2 - 2 = 0 \] ### Step 2: Calculate the right-hand derivative \( f'(2+0) \) To find \( f'(2+0) \), we need to use the definition of the derivative: \[ f'(2+0) = \lim_{h \to 0^+} \frac{f(2+h) - f(2)}{h} \] For \( x > 2 \), the function is defined as \( f(x) = 3x - x^2 \). Thus, we calculate: \[ f(2+h) = 3(2+h) - (2+h)^2 = 6 + 3h - (4 + 4h + h^2) = 2 - h - h^2 \] Now substituting into the derivative limit: \[ f'(2+0) = \lim_{h \to 0^+} \frac{(2 - h - h^2) - 0}{h} = \lim_{h \to 0^+} \frac{2 - h - h^2}{h} \] \[ = \lim_{h \to 0^+} \left( \frac{2}{h} - 1 - h \right) \] As \( h \to 0^+ \), \( \frac{2}{h} \to \infty \). Therefore, \( f'(2+0) \) does not exist. ### Step 3: Calculate the left-hand derivative \( f'(2-0) \) Now we calculate \( f'(2-0) \): \[ f'(2-0) = \lim_{h \to 0^+} \frac{f(2-h) - f(2)}{-h} \] For \( x < 2 \), the function is defined as \( f(x) = 2 - x \). Thus, we calculate: \[ f(2-h) = 2 - (2-h) = h \] Now substituting into the derivative limit: \[ f'(2-0) = \lim_{h \to 0^+} \frac{h - 0}{-h} = \lim_{h \to 0^+} -1 = -1 \] ### Conclusion We have found: - \( f'(2+0) \) does not exist (it approaches infinity). - \( f'(2-0) = -1 \). Thus, the statements are: 1. \( f'(2+0) \) does not exist. (True) 2. \( f'(2-0) \) does exist. (False) Therefore, only the first statement is correct. ### Final Answer: Only statement 1 is correct. ---

To solve the problem, we need to analyze the function \( f(x) \) defined as follows: \[ f(x) = \begin{cases} 2 - x & \text{for } 1 \leq x \leq 2 \\ 3x - x^2 & \text{for } x > 2 \end{cases} ...
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NDA PREVIOUS YEARS-FUNCTIONS, LIMIT, CONTINUITY AND DIFFERENTIABILITY-MCQs
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