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Write the Derivative of F (X) = 3 |2 + X| at X = −3.

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Question

Write the derivative of f (x) = 3 |2 + x| at x = −3. 

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Solution

\[\text{ Let } x = -3\]
\[\text{ We know }:\]
\[-3<-2\]
\[\text{ Thus, we have }:\]
\[x<-2\]
\[\text{ It gives } x+2<0.\]
\[ \therefore \left| 2 + x \right| = \left| x + 2 \right| = - \left( x + 2 \right) = - x - 2\]
\[f\left( x \right) = 3 \left| 2 + x \right| = 3\left( - x - 2 \right) = - 3x - 6\]
\[f'\left( x \right) = - 3\frac{d}{dx}\left( x \right) - \frac{d}{dx}\left( 6 \right) = - 3\]

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Chapter 30: Derivatives - Exercise 30.6 [Page 47]

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R.D. Sharma Mathematics [English] Class 11
Chapter 30 Derivatives
Exercise 30.6 | Q 12 | Page 47

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