Class CBSE Class 12 Mathematics Derivatives Q #1274
KNOWLEDGE BASED
UNDERSTAND
3 Marks 2024 AISSCE(Board Exam) SA
Show that: $\frac{d}{dx}(|x|)=\frac{x}{|x|},x\ne0$

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Detailed Solution

Step 1: Define the absolute value function

The absolute value function is defined as: $$|x| = \begin{cases} x, & \text{if } x > 0 \\ -x, & \text{if } x < 0 \end{cases}$$ Note that the function is not differentiable at $x=0$.

Step 2: Differentiate for $x > 0$

If $x > 0$, then $|x| = x$. Therefore, $$\frac{d}{dx}(|x|) = \frac{d}{dx}(x) = 1$$ Also, if $x > 0$, then $\frac{x}{|x|} = \frac{x}{x} = 1$. Thus, for $x > 0$, $\frac{d}{dx}(|x|) = \frac{x}{|x|}$.

Step 3: Differentiate for $x < 0$

If $x < 0$, then $|x| = -x$. Therefore, $$\frac{d}{dx}(|x|) = \frac{d}{dx}(-x) = -1$$ Also, if $x < 0$, then $\frac{x}{|x|} = \frac{x}{-x} = -1$. Thus, for $x < 0$, $\frac{d}{dx}(|x|) = \frac{x}{|x|}$.

Step 4: Conclusion

Since $\frac{d}{dx}(|x|) = \frac{x}{|x|}$ for both $x > 0$ and $x < 0$, we can conclude that $$\frac{d}{dx}(|x|) = \frac{x}{|x|}, \quad x \ne 0$$

Final Answer: $\frac{d}{dx}(|x|)=\frac{x}{|x|},x\ne0$

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Pedagogical Audit
Bloom's Analysis: This is an UNDERSTAND question because it requires the student to demonstrate understanding of the definition of absolute value and differentiation.
Knowledge Dimension: CONCEPTUAL
Justification: The question requires understanding of the concepts of absolute value function and differentiation.
Syllabus Audit: In the context of CBSE Class 12, this is classified as KNOWLEDGE. It is a standard textbook problem on differentiation of absolute value functions.