en.wikipedia.org/wiki/Area_of_a_circle

In geometry, the area enclosed by a circle of radius r is πr2. Here the Greek letter π represents a constant, approximately equal to 3.14159, which is equal to the ratio of the circumference of any circle to its diameter. One method of deriving this formula, which originated with Archimedes, ...

www.khanacademy.org/math/basic-geo/basic-geo-area-and-perimeter/area-circumference-circle/v/area-of-a-circle

The area of a circle is pi times the radius squared (A = π r²). Learn how to use this formula to find the area of a circle when given the diameter.

www.mathwarehouse.com/geometry/circle/area-of-circle.php

Area of a circle, formula for area explained with examples, pictures, interactive examples and quiz.

www.mathgoodies.com/lessons/vol2/circle_area.html

Area of a circle is presented in this interactive lesson from Math Goodies. ... In the last lesson, we learned that the formula for circumference of a circle is: C ...

www.virtualnerd.com/pre-algebra/perimeter-area-volume/circles/circle-sector-area-examples/circle-area-formula

www.mathsisfun.com/geometry/circle-area.html

Area of a Circle. Calculator. Enter the radius, diameter, circumference or area of a Circle to find the other three. The calculations are done "live":.

www.bbc.co.uk/schools/gcsebitesize/maths/geometry/circlesrev3.shtml

Area of a circle. There is only one formula for the area of a circle: A = π r2. We must therefore remember to use the radius each time. Question. Find the area of a ...

www.1728.org/diamform.htm

Formulas for Circle Circumference, Circle Area, Sphere Area, Partially Filled Sphere Area, Partially Filled Sphere Volume, Sphere Volume, Cylinder Area, ...

www.mathopenref.com/circlearea.html

Given the radius of a circle, the area inside it can be calculated using the formula. Area. = π. R. 2. where: R is the radius of the circle π is Pi, approximately 3.142.