Area of a circle - 8th Sep 2008
Today we looked at how to find the area of a circle.
We started by seeing that if you cut a circle up into lots of segments and place them next to each other you get a shape that looks like a rectangle. The more segments the circle is divided into to closer to a rectangle it becomes.
The width of the rectangle is the same as the radius of the circle and the length of the rectangle is half of the circumference of the circle. The circumference is 2∏r so half the circumference is ∏r.
The formula for the area of the circle is then the same the area of this rectangle, which is ∏r x r
So the area of a circle is found by the formula:
Area of circle = ∏r x r = ∏r²
For example:
To find the area of this circle with radius 4cm
Area = ∏r²
Area = ∏ x 4²
Area = ∏ x 16
Area = 50.3 cm² (1dp)
For more details, example and questons to try visit the Mymaths lesson on area of a circle
[...] to work out the surface area you find the area of the circle, double it for the two circles. Then find the area of the rectangle and add together all three to [...]