Class CBSE Class 12 Mathematics Applications of Integrals Q #873
COMPETENCY BASED
APPLY
3 Marks 2023 SA
Find the area of the following region using integration: {(x,y): y² ≤ 2x and y ≥ x-4}

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Step-by-Step Solution

1. Sketch the region:

First, sketch the curves y² = 2x and y = x - 4. This helps visualize the region whose area we need to find.

2. Find the points of intersection:

To find where the curves intersect, solve the equations simultaneously:

Substitute x = y + 4 into y² = 2x:

y² = 2(y + 4)

y² = 2y + 8

y² - 2y - 8 = 0

(y - 4)(y + 2) = 0

So, y = 4 or y = -2.

When y = 4, x = y + 4 = 4 + 4 = 8. Point of intersection: (8, 4)

When y = -2, x = y + 4 = -2 + 4 = 2. Point of intersection: (2, -2)

3. Set up the integral:

We will integrate with respect to y. The area A is given by:

A = ∫[from -2 to 4] (x_right - x_left) dy

Here, x_right is the x-value of the parabola y² = 2x, so x_right = y²/2.

And x_left is the x-value of the line y = x - 4, so x_left = y + 4.

Therefore, A = ∫[from -2 to 4] (y²/2 - (y + 4)) dy

4. Evaluate the integral:

A = ∫[from -2 to 4] (y²/2 - y - 4) dy

A = [y³/6 - y²/2 - 4y] evaluated from -2 to 4

A = [(4³/6 - 4²/2 - 4*4) - ((-2)³/6 - (-2)²/2 - 4*(-2))]

A = [(64/6 - 16/2 - 16) - (-8/6 - 4/2 + 8)]

A = [(32/3 - 8 - 16) - (-4/3 - 2 + 8)]

A = [32/3 - 24] - [-4/3 + 6]

A = 32/3 - 24 + 4/3 - 6

A = 36/3 - 30

A = 12 - 30

A = -18

Since area cannot be negative, we take the absolute value.

Correct Answer: 18 square units

Pedagogical Audit
Bloom's Analysis: This is an APPLY question because it requires the student to apply the concepts of integration to find the area bounded by curves. They need to set up the integral correctly based on the given equations and then evaluate it.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the student to follow a specific procedure: sketching the curves, finding intersection points, setting up the definite integral, and then evaluating it. It's about knowing 'how' to solve this type of problem.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. The question assesses the student's ability to apply the concept of integration to a specific problem, requiring them to integrate and find the area. It is not a straight recall from the textbook.

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