Question:medium

Find the total area of the bounded region enclosed between the parabola curve \( y^2 = 8x \) and its vertical latus rectum boundary line.

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You can save valuable time during your test by using this parabola integration shortcut: the total area enclosed between any standard parabola \( y^2 = 4ax \) and its latus rectum line is always exactly \( \frac{8}{3}a^2 \).
Updated On: Jun 3, 2026
  • \( \frac{32}{3} \text{ square units} \)
  • \( \frac{16}{3} \text{ square units} \)
  • \( 8 \text{ square units} \)
  • \( \frac{64}{3} \text{ square units} \)
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The Correct Option is A

Solution and Explanation

Step 1: Understanding the Concept:
Area under a curve is typically calculated by integrating the function between its boundary points.
For a parabola \(y^2 = 4ax\), the latus rectum is a special line perpendicular to the axis of symmetry, passing through the focus.
The coordinates of the focus are \((a, 0)\), so the equation of the latus rectum is the vertical line \(x = a\).
Step 2: Key Formula or Approach:
1. Compare the given equation \(y^2 = 8x\) to the standard form \(y^2 = 4ax\).
2. Identify the value of \(a\) to find the boundary limit.
3. Total area = \(2 \times\) (Area of the upper half).
Step 3: Detailed Explanation:
Compare \(y^2 = 8x\) with \(y^2 = 4ax\):
\(4a = 8 \implies a = 2\).
The latus rectum line is \(x = 2\). The vertex is at \((0, 0)\). So, the limits of integration are from \(x = 0\) to \(x = 2\).
The equation for the upper half of the parabola is \(y = \sqrt{8x} = \sqrt{4 \times 2x} = 2\sqrt{2}\sqrt{x}\).
Set up the area integral:
\[ \text{Total Area} = 2 \int_{0}^{2} y \, dx = 2 \int_{0}^{2} 2\sqrt{2} x^{\frac{1}{2}} dx \]
\[ = 4\sqrt{2} \int_{0}^{2} x^{\frac{1}{2}} dx \]
Apply the power rule for integration (\(\int x^n dx = \frac{x^{n+1}}{n+1}\)):
\[ = 4\sqrt{2} \left[ \frac{x^{\frac{3}{2}}}{\frac{3}{2}} \right]_{0}^{2} = 4\sqrt{2} \cdot \frac{2}{3} \left[ x^{\frac{3}{2}} \right]_{0}^{2} \]
\[ = \frac{8\sqrt{2}}{3} (2^{\frac{3}{2}} - 0) \]
Note that \(2^{\frac{3}{2}} = \sqrt{2^3} = \sqrt{8} = 2\sqrt{2}\):
\[ = \frac{8\sqrt{2}}{3} \cdot 2\sqrt{2} = \frac{16 \cdot 2}{3} = \frac{32}{3} \]
Step 4: Final Answer:
The total bounded area is \(\frac{32}{3}\) square units, which is option (A).
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