Class CBSE Class 12 Mathematics Applications of Integrals Q #1326
COMPETENCY BASED
REMEMBER
5 Marks 2024 AISSCE(Board Exam) LA
Sketch the graph of $y=x|x|$ and hence find the area bounded by this curve, X-axis and the ordinates $x=-2$ and $x=2,$ using integration.

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Detailed Solution

Step 1: Define the function

The function is given by $y = x|x|$. We can rewrite this function as a piecewise function:

$$y = \begin{cases} x^2, & \text{if } x \geq 0 \\ -x^2, & \text{if } x < 0 \end{cases}$$

Step 2: Sketch the graph

For $x \geq 0$, the graph is the parabola $y = x^2$. For $x < 0$, the graph is the parabola $y = -x^2$. The graph is symmetric about the origin.

Step 3: Set up the integral for the area

We want to find the area bounded by the curve $y = x|x|$, the x-axis, and the ordinates $x = -2$ and $x = 2$. Since the function is negative for $x < 0$, we need to take the absolute value of the integral over the interval $[-2, 0]$. The area is given by: $$A = \int_{-2}^{2} |x|x| dx = \int_{-2}^{0} |-x^2| dx + \int_{0}^{2} |x^2| dx$$ $$A = \int_{-2}^{0} -x^2 dx + \int_{0}^{2} x^2 dx$$

Step 4: Evaluate the integrals

Now, we evaluate the integrals: $$\int_{-2}^{0} -x^2 dx = \left[ -\frac{x^3}{3} \right]_{-2}^{0} = -\frac{0^3}{3} - \left( -\frac{(-2)^3}{3} \right) = 0 - \frac{8}{3} = -\frac{8}{3}$$ Since we are looking for area, we take the absolute value: $$|-\frac{8}{3}| = \frac{8}{3}$$ $$\int_{0}^{2} x^2 dx = \left[ \frac{x^3}{3} \right]_{0}^{2} = \frac{2^3}{3} - \frac{0^3}{3} = \frac{8}{3} - 0 = \frac{8}{3}$$

Step 5: Calculate the total area

The total area is the sum of the absolute values of the integrals: $$A = \frac{8}{3} + \frac{8}{3} = \frac{16}{3}$$

Final Answer: 16/3

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Pedagogical Audit
Bloom's Analysis: This is an REMEMBER question because it requires recalling the definition of absolute value, sketching graphs of basic functions, and applying integration techniques.
Knowledge Dimension: CONCEPTUAL
Justification: Understanding the concept of absolute value and its impact on the function's graph, as well as the concept of area under a curve using integration, is crucial for solving this problem.
Syllabus Audit: In the context of CBSE Class 12, this is classified as Application of Integrals. It involves using integration to find the area under a curve, which is a standard application of integral calculus.