This short video and interactive assessment activity is designed to teach third graders about identifying the properties of rectangles.

This short video and interactive assessment activity is designed to teach third graders about identifying the properties of squares.

This short video and interactive assessment activity is designed to teach fifth graders about identifying the properties of squares.

This task shows how to inscribe a circle in a triangle using angle bisectors. A companion task, ``Inscribing a circle in a triangle II'' stresses the auxiliary remarkable fact that comes out of this task, namely that the three angle bisectors of triangle ABC all meet in the point O.

This task is primarily for instructive purposes but can be used for assessment as well. Parts (a) and (b) are good applications of geometric constructions using a compass and could be used for assessment purposes but the process is a bit long since there are six triangles which need to be constructed.

This task provides an opportunity for students to apply triangle congruence theorems in an explicit, interesting context.

This problem introduces the circumcenter of a triangle and shows how it can be used to inscribe the triangle in a circle. It also shows that there cannot be more than one circumcenter.

This task focuses on a remarkable fact which comes out of the construction of the inscribed circle in a triangle: the angle bisectors of the three angles of triangle ABC all meet in a point.

The applets in this Interactive Geometry Dictionary (IGD) will allow students an opportunity to explore finding the area of some common shapes. The applets demonstrate how to find the area of a triangle using the area of a parallelogram, which in turn can be found using the area of a rectangle. This tool also supports the lesson "What's My Area" cataloged separately.

In this lesson students are introduced to various types of symmetry. After exploring the symmetries that exist with letters of the alphabet, they make inversions of their own name. Suggestions for implementation and support materials are provided.

This Java interactive tool can be used to create dynamic drawings on an isometric dot grid, and to explore volume, surface area, and congruence concepts. Users can draw figures using edges, faces, or cubes and can shift, rotate, color, decompose, and view figures in 2‑D or 3‑D with this applet. Instructions on using and exploring with the tool are included on the page. A related multi-lesson unit from Illuminations for middle school students is linked to the side.

This task is closely related to very important material about similarity and ratios in geometry.

In this 4-lesson unit, students identify, compare, and analyze attributes of two- and three-dimensional shapes, and develop geometric vocabulary. Students use basic linear measurement, understand and create scale representations, and explore perimeter and area measurement as they design their clubhouses. Activity sheets (pdf), lesson extensions and other commentary are provided.

The activities in this four-lesson unit enable students to use their knowledge of number, measurement, and geometry to solve interesting problems. Planning and visualizing, estimating and measuring, and testing and revising are components of the ladybug activities. Students design "virtual paths" that enable a ladybug to either hide under a leaf or go through a maze. They develop navigational skills by testing their path and revising it. Two interactive Java applets (Ladybug Mazes and Hiding Ladybug, cataloged separately) support student solutions.

In addition to the purely geometric and trigonometric aspects of the task, this problem asks students to model phenomena on the surface of the earth.

This is an instructional task that gives students a chance to reason about lines of symmetry and discover that a circle has an an infinite number of lines of symmetry. Even though the concept of an infinite number of lines is fairly abstract, fourth graders can understand infinity in an informal way.

This task provides students a chance to experiment with reflections of the plane and their impact on specific types of quadrilaterals. It is both interesting and important that these types of quadrilaterals can be distinguished by their lines of symmetry.

This task is intended for instruction, providing the students with a chance to experiment with physical models of triangles, gaining spatial intuition by executing reflections.

This sequence of four lessons is designed to help students to understand ratio, proportion, scale factor, and similarity. Using online activities, they compare the perimeter and area ratios of similar rectangles with various scale factors; work with scale factor and surface area of various rectangular prisms; explore the relationship between the volume of two similar rectangular prisms; and examine the connection between the surface area of two similar rectangular prisms. All instructions, needed links, and activity sheets are provided.