This short video and interactive assessment activity is designed to teach third graders about counting the number of basic 2d shapes in a composite figure.

This short video and interactive assessment activity is designed to teach second graders about counting the number of different 2d shapes in a composite figure.

This short video and interactive assessment activity is designed to teach second graders about identifying parallel and perpendicular lines.

This short video and interactive assessment activity is designed to teach second graders an overview of quarter-circles and semi-circles.

This short video and interactive assessment activity is designed to teach third graders an overview of quarter-circles and semi-circles.

This short video and interactive assessment activity is designed to give fourth graders an overview of quarter-circles and semi-circles.

This short video and interactive assessment activity is designed to teach third graders an overview of reflective symmetry.

This short video and interactive assessment activity is designed to teach first graders an overview of quarter-circles and semi-circles.

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

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 inscribed angle of a circle - the angle subtended at the periphery by two points on the circle. The applet presents a circle with three points on it that can be dragged. The inscribed angle is shown and demonstrates that it is constant as the vertex is dragged. Links to other related topics such as Thales Theorem. 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 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.

Great activities sorted by grade - you can also sort them by subject by selecting that in the top left corner!
For Grades 3-12 & ungraduate.

An interactive applet and associated web page that demonstrate the intercept (b) of a line. The applet has two points that define a line. As the user drags either point it continuously recalculates the intercept, the point where the line crosses the y-axis at x=0. Can be used in conjunction with the slope to derive the equation of a line. The grid, axis pointers and coordinates can be turned on and off. The intercept calculation can be turned off to permit class exercises and then turned back on the verify the answers. The applet can be printed as it appears on the screen to make handouts. The web page has a full description of the concept of intercept, a worked example and has links to other pages relating to coordinate geometry. 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 the intercepted arc - 'That part of a circle that lies between two lines that intersect it'. The applet shows a circle with part of it's circumference highlighted and the central angle shown. As the user drags either end of the arc it is redrawn and the intercpted arc changes. 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 interior angles that are formed where a transversal crosses two lines. The applets shows the two possible pairs of angles in turn when in animation mode. By dragging the three lines, it can be seen that the angles are supplementary only when the lines are parallel. When not in animated mode, there is a button that alternates the two pairs of angles. The text on the page discusses the properties of the angle pairs both in the parallel and non-parallel cases. 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.