Question:medium

The area of the region bounded by the curves \( x = y^2 - 2 \) and \( x = y \) is

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When the boundary curves are expressed as \(x = f(y)\), it is often much easier to integrate with respect to \(y\) (Horizontal strips) to avoid splitting the integral into multiple parts.
Updated On: Apr 16, 2026
  • \( \frac{9}{4} \)
  • 9
  • \( \frac{9}{2} \)
  • \( \frac{9}{7} \)
Show Solution

The Correct Option is C

Solution and Explanation

Step 1: Understanding the Concept:
To find the area bounded by a left curve $x = f(y)$ and a right curve $x = g(y)$, we integrate with respect to $y$. The area is given by the integral of $(\text{Right Curve} - \text{Left Curve})$ evaluated between their points of intersection.
Step 2: Key Formula or Approach:
The area $A$ is given by: \[ A = \int_{y_1}^{y_2} [g(y) - f(y)] \, dy \] where $g(y)$ is the curve on the right and $f(y)$ is the curve on the left.
Step 3: Detailed Explanation:
First, find the points of intersection by setting the equations equal to each other: \[ y^2 - 2 = y \] \[ y^2 - y - 2 = 0 \] Factor the quadratic equation: \[ (y - 2)(y + 1) = 0 \] Thus, the points of intersection are at $y = -1$ and $y = 2$.
Next, determine which curve is on the right (has larger $x$ values) in the interval $(-1, 2)$. Pick a test point, say $y = 0$: For the line $x = y$, $x = 0$. For the parabola $x = y^2 - 2$, $x = -2$. Since $0>-2$, the line $x = y$ is the right curve, and the parabola $x = y^2 - 2$ is the left curve.
Set up the integral for the area: \[ A = \int_{-1}^{2} [y - (y^2 - 2)] \, dy \] \[ A = \int_{-1}^{2} (-y^2 + y + 2) \, dy \] Integrate term by term: \[ A = \left[ -\frac{y^3}{3} + \frac{y^2}{2} + 2y \right]_{-1}^{2} \] Evaluate the definite integral at the upper limit ($y = 2$): \[ \left( -\frac{8}{3} + \frac{4}{2} + 4 \right) = -\frac{8}{3} + 2 + 4 = 6 - \frac{8}{3} = \frac{10}{3} \] Evaluate at the lower limit ($y = -1$): \[ \left( -\frac{(-1)^3}{3} + \frac{(-1)^2}{2} + 2(-1) \right) = \frac{1}{3} + \frac{1}{2} - 2 = \frac{5}{6} - \frac{12}{6} = -\frac{7}{6} \] Subtract the lower limit value from the upper limit value: \[ A = \frac{10}{3} - \left( -\frac{7}{6} \right) = \frac{20}{6} + \frac{7}{6} = \frac{27}{6} \] Simplify the fraction: \[ A = \frac{9}{2} \] Step 4: Final Answer:
The area of the region bounded by the curves is $\frac{9}{2}$. The correct option is (C).
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