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Show that F ( X ) = { 12 X − 13 If X ≤ 3 2 X 2 + 5 If X > 3 is Differentiable at X = 3. Also, Find F'(3). - Mathematics

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प्रश्न

Show that \[f\left( x \right) =\]`{(12x, -,13, if , x≤3),(2x^2, +,5, if x,>3):}` is differentiable at x = 3. Also, find f'(3).

संक्षेप में उत्तर
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उत्तर

Given:  

show that \[f\left( x \right) =\]`{(12x, -,13, if , x≤3.),(2x^2, +,5, if x,>3.):}`

We have to show that the given function is differentiable at x = 3.

We have,

(LHD at x=3) = 

\[\lim_{x \to 3^-} \frac{f(x) - f(3)}{x - 3}\]

\[= \lim_{x \to 3} \frac{12x - 13 - 23}{x - 3}\]
\[ = \lim_{x \to 3} \frac{12x - 36}{x - 3}\]
\[ = \lim_{x \to 3} \frac{12 (x - 3)}{x - 3}\]
\[ = \lim_{x \to 3} 12 \]
\[ = 12\]

(RHD at = 3) = 

\[\lim_{x \to 3^+} \frac{f(x) - f(3)}{x - 3}\]

\[= \lim_{x \to 3} \frac{2 x^2 + 5 - 23}{x - 3}\]
\[ = \lim_{x \to 3} \frac{2 x^2 - 18}{x - 3}\]
\[ = \lim_{x \to 3} \frac{2 ( x^2 - 9)}{x - 3}\]
\[ = \lim_{x \to 3} 2(x + 3) \]
\[ = 2 \times 6 \]
\[ = 12\]

Thus, (LHD at x=3) = (RHD at x=3) = 12.
So, 

\[f(x)\] is differentiable at x=3 and 
\[f'(3) = 12 .\]
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अध्याय 10: Differentiability - Exercise 10.1 [पृष्ठ १०]

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आरडी शर्मा Mathematics [English] Class 12
अध्याय 10 Differentiability
Exercise 10.1 | Q 3 | पृष्ठ १०

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