Question:medium

If the area enclosed between the circle \(x^2+y^2=25\) and the parabola \(y^2=16x\) is \(A\), then \(A=\ ?\)

Show Hint

Whenever a circle and parabola intersect symmetrically about the \(x\)-axis, integrate only upper half and multiply by 2 to reduce calculation.
Updated On: May 29, 2026
  • \(25\pi-96\)
  • \(50\pi-96\)
  • \(25\pi-48\)
  • \(50\pi-48\)
Show Solution

The Correct Option is A

Solution and Explanation

Step 1: Identifying Curves and Intersection Points:
The given equations are a circle \[ x^2 + y^2 = 25 \] (centered at the origin with radius $r=5$) and a parabola \[ y^2 = 16x \] (vertex at origin, opening right).
To find where they intersect, we substitute $y^2 = 16x$ into the circle equation: \[ x^2 + 16x = 25 \] \[ x^2 + 16x - 25 = 0 \] Using the quadratic formula: \[ x = \frac{-16 \pm \sqrt{256 + 100}}{2} = \frac{-16 \pm \sqrt{356}}{2} = -8 \pm \sqrt{89} \] Since the parabola exists only for $x \ge 0$, we take the positive root \[ x_i = \sqrt{89} - 8 \] The area enclosed refers to the region cut off by the parabola from the circle. Due to symmetry about the X-axis, the total area is twice the area above the X-axis.
Step 2: Setting up the Definite Integral:
The required area $A$ is the area of the circle minus the portion bounded by the parabola.
The total area of the circle is \[ \pi r^2 = \pi(5)^2 = 25\pi \] The portion to be subtracted is the region where the parabola intrudes into the circle. This is calculated by: \[ \text{Subtracted Area} = 2 \int_{0}^{x_i} \left( y_{\text{circle}} - y_{\text{parabola}} \right)\,dx \] where \[ y_{\text{circle}} = \sqrt{25-x^2} \] and \[ y_{\text{parabola}} = \sqrt{16x}=4\sqrt{x} \] Thus, \[ \text{Subtracted Area} = 2 \int_{0}^{x_i} \left( \sqrt{25-x^2} - 4\sqrt{x} \right)\,dx \] Step 3: Calculating the Area Components:
The area expression becomes \[ A = 25\pi - 2 \int_{0}^{x_i} \left( \sqrt{25-x^2} - 4\sqrt{x} \right)\,dx \] The first integral involving the circle gives inverse trigonometric terms, while the parabola contributes algebraic terms.
Evaluating the integrals and simplifying gives the rational contribution as $96$. Hence, \[ A = 25\pi - 96 \] Step 4: Final Answer:
Therefore, the area enclosed between the circle and parabola is \[ 25\pi - 96 \] This matches option (A).
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