An interactive applet and associated web page that the definition of the center of a regular polygon. The applet presents a regular polygon, where the user can drag any vertex to resize it, and change the number of sides. The center point is shown to always be the point equidistant from every vertex. 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 define and illustrate the central angle of a polygon. The applet shows the angle and users can experiment by changing the number of sides and resizing the polygon. The web page has a description and a formula for the central angle given the number of sides. 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 show the properties of a circumcircle of a polygon. The applet shows a regular polygon where the user can drag the vertices to reshape it and alter the number of sides. As the polygon is being varied, the circumcircle is shown, passing through all vertices. The text describes two ways to calculate the radius of the circumcircle, depending on what you are given to start. 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 concept of a concave polygon - one where at least one interior angle is greater than 180 degrees. The applet shows an irregular polygon initially with one interior angle greater than 180 degrees. The user can drag any vertex and change the number of sides in the range 3..99. When the polygon is concave, the angles that make it so are drawn in red. The goal is to show through experimentation what the concept of concavity really means. 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 congruence of polygons. The applet presents nine polygons that are in fact congruent, but don't look it because they are reflected and rotated in various ways. If you click on one, it rotates and flips as needed, then slides over the top of another to show it is congruent. The web page describes how to determine if two polygons are congruent. 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 concept of a convex polygon - one where all interior angle are less than 180 degrees. The applet shows an irregular convex polygon initially. The user can drag any vertex, change the number of sides in the range 3..99, and make it regular or irregular. When the polygon is convex, the polygon is so flagged. It is shown that regular polygons are always convex. The goal is to show through experimentation what the concept of convexity really means. 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.

The purpose of this lesson is to explore using nets to represent prisms.

Included is a YouTube video to support Grade 8 Blended Learning Math - Unit 4.1: Measuring Prisms and Cylinders - Exploring Nets.

A web page and interactive applet illustrating the properties of a decagon (10 sided polygon). The applet shows a decagon where the user can drag any vertex to reshape it. User can see that the interior and exterior angles are constant in a regular decagon, but vary in an irregular version. Controls allow the display or hiding of the diagonals, and triangles within the decagon. The web page lists the properties of a decagon including interior angles, exterior angles, sum of exterior angles, area, number of diagonals and number of internal triangles. Links to pages with generalized properties of all polygons. 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 illustrating the properties of a dodecagon (10 sided polygon). The applet shows a dodecagon where the user can drag any vertex to reshape it. User can see that the interior and exterior angles are constant in a regular dodecagon, but vary in an irregular version. Controls allow the display or hiding of the diagonals, and triangles within the dodecagon. The web page lists the properties of a dodecagon including interior angles, exterior angles, sum of exterior angles, area, number of diagonals and number of internal triangles. Links to pages with generalized properties of all polygons. 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 illustrating the properties of a heptagon (7 sided polygon). The applet shows a heptagon where the user can drag any vertex to reshape it. User can see that the interior and exterior angles are constant in a regular heptagon, but vary in an irregular version. Controls allow the display or hiding of the diagonals, and triangles within the heptagon. The web page lists the properties of a heptagon including interior angles, exterior angles, sum of exterior angles, area, number of diagonals and number of internal triangles. Links to pages with generalized properties of all polygons. 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 illustrating the properties of a hexagon (6 sided polygon). The applet shows a hexagon where the user can drag any vertex to reshape it. User can see that the interior and exterior angles are constant in a regular hexagon, but vary in an irregular version. Controls allow the display or hiding of the diagonals, and triangles within the hexagon. The web page lists the properties of a hexagon including interior angles, exterior angles, sum of exterior angles, area, number of diagonals and number of internal triangles. Links to pages with generalized properties of all polygons. 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 incircle of a polygon - The largest circle the will fit inside a polygon that touches every side. The applet shows a polygon where the user can drag any vertex and change the number of sides. As they do so, the incircle is drawn for that polygon and the radius calculation is updated. Calculation can be turned off for class discussions. The text on the web page gives two formulae for calculating the inradius, depending on the initial givens. 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 relationship of the interior and exterior angles of a polygon. The applet shows an irregular polygon where one vertex is draggable. As it is dragged the interior and exterior angles at that vertex are displayed, and a formula is continuously updated showing that they are supplementary. The tricky part is when the vertex is dragged inside the polygon making it concave. The applet shows how the relationship still holds provided you get the signs of the angles right. 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 show the behavior of irregular polygons. The applet shows initially an irregular convex polygon. All vertices are draggable and when dragged show that this has no effect on any other vertex. The polygon can be made regular, and the number of sides changed between 3 and 99. 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 illustrating the properties of a nonagon (9 sided polygon). The applet shows a nonagon where the user can drag any vertex to reshape it. User can see that the interior and exterior angles are constant in a regular nonagon, but vary in an irregular version. Controls allow the display or hiding of the diagonals, and triangles within the nonagon. The web page lists the properties of a nonagon including interior angles, exterior angles, sum of exterior angles, area, number of diagonals and number of internal triangles. Links to pages with generalized properties of all polygons. 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 illustrating the properties of a octagon (8 sided polygon). The applet shows an octagon where the user can drag any vertex to reshape it. User can see that the interior and exterior angles are constant in a regular octagon, but vary in an irregular version. Controls allow the display or hiding of the diagonals, and triangles within the octagon. The web page lists the properties of an octagon including interior angles, exterior angles, sum of exterior angles, area, number of diagonals and number of internal triangles. Links to pages with generalized properties of all polygons. 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 illustrating the properties of a pentagon (5 sided polygon). The applet shows a pentagon where the user can drag any vertex to reshape it. User can see that the interior and exterior angles are constant in a regular pentagon, but vary in an irregular version. Controls allow the display or hiding of the diagonals, and triangles within the pentagon. The web page lists the properties of a pentagon including interior angles, exterior angles, sum of exterior angles, area, number of diagonals and number of internal triangles. Links to pages with generalized properties of all polygons. 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 perimeter of a polygon. A polygon is shown that can be resized by dragging its vertices. As you drag, the perimeter is continuously recalculated. Text on the page explains that the perimeter is the sum of the sides. For those who prefer it, in a formula that is given. 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 reference book project at http://www.mathopenref.com.

An interactive applet and associated web page that demonstrate polygons. The applet shows a polygon which is initially an irregular convex pentagon. The user can drag any vertex and a message shows if it becomes concave. The user can also alter the number of sides from 3 to 99, the title changing to reflect it's name up to 12 sides. You can also make it regular, dragging a vertex then changes all vertices to maintain it as regular. The web page has many definitions and links to the various forms and orders of polygon. 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 that the exterior angles of a polygon always add to a constant (360 or 720 depending on your point of view). The applet shows a polygon where the user can drag the vertices to reshape it, alter the number of sides, make it convex or concave, regular or irregular. The applet shows the angle summation in real time, demonstrating that it is always constant. It also demonstrates how exterior angles are accounted for in concave polygons, where the exterior angle seems to be inside the figure. These are taken as negative angles and the sum demonstrably remains the same. 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.