Match List-I with List-II
| List-I (Region) | List-II (Area in sq. units) | ||
| (A) | Region bounded by the curve \(x = 4-y^{2}\) and the y-axis | (I) | 4 |
| (B) | Region bounded by the line x = 2y, the y-axis and the line y = 3 | (II) | \(\displaystyle\frac{9}{2}\) |
| (C) | Region bounded by the curve \(x = 3y-y^{2}\) and the y-axis | (III) | 9 |
| (D) | Region bounded by the curve x = |y| and the line x = 2 | (IV) | \(\displaystyle\frac{32}{3}\) |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A)-(IV), (B)-(III), (C)-(II), (D)-(I)
Each region lies between a curve x = g(y) and the y-axis (or a vertical line), so it is found by integrating in y.
(A) Region bounded by the curve \(x = 4-y^{2}\) and the y-axis
This matches (IV) \(\displaystyle\frac{32}{3}\).
The curve meets the y-axis where \(4-y^{2} = 0\), that is y = ±2:
\( \displaystyle A = \int_{-2}^{2}(4-y^{2})\,dy = \left[4y-\frac{y^{3}}{3}\right]_{-2}^{2} \)
\( \displaystyle = \frac{16}{3}-\left(-\frac{16}{3}\right) = \frac{32}{3} \)
(B) Region bounded by the line x = 2y, the y-axis and the line y = 3
This matches (III) 9.
The line meets the y-axis at the origin, so y runs from 0 to 3:
\( \displaystyle A = \int_{0}^{3}2y\,dy = \left[y^{2}\right]_{0}^{3} = 9 \)
(C) Region bounded by the curve \(x = 3y-y^{2}\) and the y-axis
This matches (II) \(\displaystyle\frac{9}{2}\).
Since \(3y-y^{2} = y(3-y)\), the curve meets the y-axis at y = 0 and y = 3 and lies to the right of it in between:
\( \displaystyle A = \int_{0}^{3}(3y-y^{2})\,dy = \left[\frac{3y^{2}}{2}-\frac{y^{3}}{3}\right]_{0}^{3} \)
\( \displaystyle = \frac{27}{2}-9 = \frac{9}{2} \)
(D) Region bounded by the curve x = |y| and the line x = 2
This matches (I) 4.
The curve meets x = 2 at y = ±2. For each y the width of the region is \(2-|y|\), and the region is symmetric about the x-axis:
\( \displaystyle A = 2\int_{0}^{2}(2-y)\,dy = 2\left[2y-\frac{y^{2}}{2}\right]_{0}^{2} \)
\(= 2(4-2) = 4\)