How to Determine the Center of a Circle in Geometry

A circle is perfectly round.

To find the center of a circle, knowledge of some basic concepts of geometry is required. The first is diameter, a line from one side of a circle to the the other through the center of the circle. The next is radius, a line from the center of the circle to the circle's circumference. The radius is half of the diameter. The center can be found using a right triangle and a straightedge.

Things You'll Need

• Right triangle
• Straightedge

Instructions

1. Draw a right triangle, with the right angle touching any part on the circle. Make sure the sides of the triangle that form the right angle extend beyond the circle.

2. Mark the points where the sides that form the triangle's right angle cross the circle.

3. Draw a line between these two points, using a straightedge. This is the first diameter.

4. Draw a second right triangle with the right angle touching another point on the circle.

5. Mark the points where the sides that form the triangle's right angle cross the circle.

6. Draw a line between the two marks. This is the second diameter. The point where the two diameters cross is the center of the circle.

Tips & Warnings

• Any object with a right angle can be used.

References

• Math Open Reference: Finding the Center of a Circle