An interactive applet and associated web page that demonstrate the area of a circle. A circle is shown with a point on the circumference that can be dragged to resize the circle. As the circle is resized, the radius and the area computation is shown changing in real time. The radius and formula can be hidden for class discussion. Applet can be enlarged to full screen size for use with a classroom projector. This resource is a component of the Math Open Reference Interactive Geometry textbook project at http://www.mathopenref.com.
An interactive applet and associated web page that demonstrate the area of an ellipse. The major and minor axes can be dragged and the area is continuously recalculated. The ellipse has a grid inside it so that students can estimate the area and compare the result to the calculated one. The web page has the formula for the area calculation. The web page also has links to other pages defining the various properties of an ellipse and to some ellipse constructions. Applet can be enlarged to full screen size for use with a classroom projector. This resource is a component of the Math Open Reference Interactive Geometry textbook project at http://www.mathopenref.com.
A web page and interactive applet show how to compute the area of an annulus. Text on the page explains that the area is the overall area minus the area of the circular 'hole' in the center. For those who prefer it in a formula that is given. The user can resize the two circles defining the annulus and visually estimate the area from a unit grid drawn inside it. A companion page is Definition of an Annulus at http://www.mathopenref.com/annulus.html Applet can be enlarged to full screen size for use with a classroom projector. This resource is a component of the Math Open Reference Interactive Geometry textbook project at http://www.mathopenref.com.
This geometry lesson shows how to calculate the area of a circle and discusses how pi is calculated and used in the formula. [Geometry playlist: Lesson 13 of 31]
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