Illustrative Mathematics
Finding an Unknown Angle
Teach your class how to apply their knowledge of geometry as they explore the unknown. In order to find an unknown angle, students must understand that rectangles have four interior right angles, that right angles have 90 degrees, and...
Curated OER
Triangle's Interior Angles
Given a pair of parallel lines and a triangle in between, geometers prove that the sum of the interior angles is 180 degrees. This quick quest can be used as a pop quiz or exit ticket for your geometry class.
Illustrative Mathematics
Are These Right?
Is that a right triangle or a wrong triangle? Young mathematicians look at eleven different shapes and use a measuring tool of their choice to determine which triangles have right angles. Consider cutting out sets of the shapes to...
Illustrative Mathematics
Sum of Angles in a Polygon
How can learners use algebra to solve a geometry problem? Help learners create an equation that shows the relationship between the number of sides of a polygon and the sum of the interior angles. Students are asked to divide the...
Illustrative Mathematics
Find the Missing Angle
This one activity requires young geometers to pull together information they are currently learning with things they have learned previously. Here they rely on understanding something about parallel lines, alternative interior angles,...
Curated OER
Tile Patterns II: Hexagons
After learning that the sum of interior angles for triangles is 108 degrees, take it further to show that the sum of angles in any polygon is the same! Using hexagons, pupils practice finding the measure of the six congruent angles. Make...
Curated OER
Star Wars: Rays and Angles Edition
Rays and angles and Star Wars? It sounds strange, but it's actually a fun game to help fourth graders get good at measuring and identifying angles and rays with a protractor. Each pair of children chooses which Star Wars character they'd...
101 Questions
Marine Ramp
Boat ramps move with waves and changes in water level. Scholars decide on the proper length for a ramp so the angle connecting both sides is appropriate. They visualize the situation and use a simulation to view the results with their...
Illustrative Mathematics
Regular Tessellations of the Plane
Bringing together the young artists and the young organizers in your class, this lesson plan takes that popular topic of tessellations and gives it algebraic roots. After covering a few basic properties and definitions, learners attack...
Curated OER
Why Does ASA Work?
Your geometry learners explore Angle-Side-Angle congruence in this collaborative task. The sum of the interior angles of all triangles being one hundred eighty degrees, is the key learners will discover as they explain their reasoning...
Illustrative Mathematics
Seven Circles III
A basic set-up leads to a surprisingly complex analysis in this variation on the question of surrounding a central circle with a ring of touching circles. Useful for putting trigonometric functions in a physical context, as well as...
Illustrative Mathematics
Eratosthenes and the Circumference of the Earth
The class gets to practice being a mathematician in ancient Greece, performing geometric application problems in the way of Eratosthenes. After following the steps of the great mathematicians, they then compare the (surprisingly...
Curated OER
Inscribing a Hexagon in a Circle
This activity is a follow-on activity to inscribing a square in a circle. The overall problem is more complex. It deals with geometric constructions, properties of triangles, and regular hexagons. The final part of the activity finds the...