Circle area from two-point radius: In the xy-plane, points P(2, 0) and Q(5, 4) are given. If a circle has radius equal to the distance PQ, find its area (use π as pi).

Difficulty: Easy

Correct Answer: 25 π

Explanation:


Introduction / Context:
The question combines distance formula in the coordinate plane with the area formula for a circle. First compute the segment length PQ; that length becomes the radius r. Then evaluate area = π * r^2.


Given Data / Assumptions:

  • P = (2, 0)
  • Q = (5, 4)
  • Area of circle = π * r^2 with r = PQ


Concept / Approach:
Use r = sqrt[(x2 − x1)^2 + (y2 − y1)^2]. Then square r to compute area. This avoids working with square roots at the end since r^2 is needed directly in the area formula.


Step-by-Step Solution:

Compute differences: Δx = 5 − 2 = 3; Δy = 4 − 0 = 4.Distance squared: r^2 = 3^2 + 4^2 = 9 + 16 = 25.Thus r = 5.Area = π * r^2 = π * 25 = 25 π.


Verification / Alternative check:

The 3-4-5 right triangle is a standard Pythagorean triple; distance 5 is expected, making area 25 π immediate.


Why Other Options Are Wrong:

  • 16 π, 14 π, 32 π: These correspond to incorrect computations of r^2; only 25 π matches Δx^2 + Δy^2 = 25.


Common Pitfalls:

  • Using r instead of r^2 in the area formula or mixing up Δx and Δy.


Final Answer:

25 π

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