The purpose of this task is primarily assessment-oriented, asking students to demonstrate knowledge of how to determine the congruency of triangles.

The purpose of this task is to provide students with a multi-step problem involving volume and to give them a chance to discuss the difference between exact calculations and their meaning in a context.

This task asks students to use similarity to solve a problem in a context that will be familiar to many, though most students are accustomed to using intuition rather than geometric reasoning to set up the shot.

The purpose of this task is to help students understand what is meant by a base and its corresponding height in a triangle and to be able to correctly identify all three base-height pairs.

This short video and interactive assessment activity is designed to teach second graders an overview of lines, curves, vertices, and sides of 2d shapes.

This short video and interactive assessment activity is designed to teach third graders an overview of lines, curves, vertices, and sides of 2d shapes.

This short video and interactive assessment activity is designed to give fourth graders an overview of simple figure patterns.

This short video and interactive assessment activity is designed to teach second graders an overview of simple figure patterns.

This short video and interactive assessment activity is designed to teach third graders an overview of simple figure patterns.

An interactive applet and associated web page that provide step-by-step instructions on how to bisect a line using only a compass and straightedge. The animation can be run either continuously like a video, or single stepped to allow classroom discussion and thought between steps. 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 task provides the most famous construction to bisect a given angle. It applies when the angle is not 180 degrees.

An interactive applet and associated web page that provide step-by-step instructions on how to bisect an angle using only a compass and straightedge. The animation can be run either continuously like a video, or single stepped to allow classroom discussion and thought between steps. 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 task applies reflections to a regular hexagon to construct a pattern of six hexagons enclosing a seventh: the focus of the task is on using the properties of reflections to deduce this seven hexagon pattern.

This task applies reflections to a regular octagon to construct a pattern of four octagons enclosing a quadrilateral: the focus of the task is on using the properties of reflections to deduce that the quadrilateral is actually a square.

CK-12 Foundation gives access to high quality educational materials for K-12 students all over the world.
They have high-quality, standards-aligned, open content in the STEM subjects.

This is an OUTSTANDING resource. Be sure to check out the Math & Science FlexLets

Students - select "switch to student version" from the top menu.

A catenary is the curve created by a theoretical representation of a hanging chain or cable held at both ends.

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.

The purpose of this task is to use geometric and algebraic reasoning to model a real-life scenario. In particular, students are in several places (implicitly or explicitly) to reason as to when making approximations is reasonable and when to round, when to use equalities vs. inequalities, and the choice of units to work with (e.g., mm vs. cm).

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 demonstrate the central angle of a circle - the angle subtended at the center by two points ion the circle. The applet presents a circle with two points on it that can be dragged. The central angle is shown changing as you drag. 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.