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Reviewed CSCA Mathematics question · Easy

A circle has its center at (-1, 3) and passes through the point (2, -1). What is the length of its diameter?

  1. 5
  2. 10
  3. 25
  4. √5
Show the answer and explanation

Correct answer

B. 10

Principle or equation

The radius of a circle is the distance from the center to any point on the circle. The diameter is twice the radius.

Why this answer is correct

Distance between center (-1,3) and point (2,-1) is sqrt((2 - (-1))^2 + (-1 - 3)^2) = sqrt(3^2 + (-4)^2) = sqrt(9 + 16) = sqrt(25) = 5. So radius = 5, diameter = 2 * 5 = 10.

Example

If center (0,0) and point (3,4), radius = 5, diameter = 10.

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