How to Find the Area of a Semi-Circle
Finding the area of a semi-circle, or half a perfect circle, is a basic skill in the field of geometry. To determine the area of a semi-circle, you must know the value of pi (π), which is roughly 3.14. In any perfect circle, the circumference is exactly the length of the diameter times π. All you need to know to find the area of a semi-circle is the length of its radius.
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Instructions
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Measure the radius of the semi-circle with a ruler or other measuring device. The radius starts at the middle point of the semi-circle's straight line and runs directly to the center of the curved side. It can be measured also from the center either to the right or to the left ends of the straight line.
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Use the length of the radius to find the area of a circle with that radius using the following formula: pi times the radius squared. For example, with a 2-inch radius, the area of the circle is roughly 12.56 square inches.
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Multiply the result by half to determine the area of the semi-circle.
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Tips & Warnings
Make sure you measure the radius correctly. Use the protractor and run the line of the radius at a 90 degree angle to the straight line of the semi-circle, starting at the line's center and running to the midpoint of the curve.
References
- Photo Credit steel ruler image by dwags from Fotolia.com
