All triangles have some things in common. Using these properties of triangles, learners find missing angle measures. Scholars use the Angle Sum Property and properties of special triangles throughout the lesson.

One of the basic properties of inscribed angles gets a triangle proof treatment in a short but detailed exercise. Leading directions take the learner through identifying characteristics of a circle and how they relate to angles and...

Logical thinking is at the forefront of this jam-packed lesson, with young mathematicians not only investigating geometric concepts but also how they "know what they know". Through each activity and worksheet, learners wrestle with...

More than just a worksheet, the resource provides a thorough guide to navigate through the land of parallelograms. Filled with definitions and theorems, the resource supports learners through problems such as proofs and finding missing...

Building on young mathematicians' prior knowledge of three-sided shapes, this instructional activity series explores the defining characteristics of different types of triangles. Starting with a shared reading of the children's...

Can any three side lengths create a triangle? Your classes tackle this question and more in the 11th lesson of the 29-part module. Through modeling with patty paper, individuals discover the relationship between the lengths of the sides...

How does the number of sides of a polygon affect the angle measures? Learners recognize a pattern in finding the total measure of interior and exterior angles and the number of diagonals. They use the patterns to calculate...

Angles and triangles: they're all connected. Uncover the connections between angles in triangles. Scholars learn how to find both exterior and interior angle measures in triangles. The lesson emphasizes the vocabulary related to these...

Challenge the class with inscribed circles in triangles. The assessment task requests class members use their knowledge of circles and right triangles to prove two triangles are congruent. They go on to utilize their knowledge of...

Do your learners always, sometimes, or never remember the properties of the segments in triangles? Get that number closer to always with a creative lesson analyzing all four segments. Scholars consider a statement about one of the...

What does it take to show two triangles are similar? The 11th segment in a series of 16 introduces the AA Criterion for Similarity. A discussion provides an informal proof of the theorem. Exercises and problems require scholars to apply...

Enjoy this nicely organized activity that puts together multiple problems regarding trapezoid proofs. The resource can be used as a guide that begins with proving properties and ends with solving for measures of line segments.

Review for the test with a comprehensive list of terms and concepts for the unit on congruence and similarity. It divides divides the sections in the order of the lessons presented during the unit. 

Stuck trying to remember the formal language of a geometric proof? Never fear, this handout has them all ready to go. The reasons are sectioned by topic so this handy guide is ready when you are to tackle those two column proofs. 

Find missing angle measures using the properties of triangles. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video, or receive hints.

This lesson focuses on the Triangle Inequality, when the sum of the lengths of any two sides of a triangle is greater than the length of the third. When this happens, the three sides cannot form a triangle.