How can you prove it? Guide classes through an exploration of two possible triangle congruence criteria: AAS and HL. Learners connect this criteria to those previous learned and also explore criteria that does not work. The lesson...

Your learners connect the new concepts of transformations in the coordinate plane to their previous knowledge using the solid vocabulary development in this unit. Like a foreign language, mathematics has its own set of vocabulary terms...

What do you need to prove triangles are similar? Learners answer this question through a construction exploration. Once they establish the criteria, they use the congruence and proportionality properties of similar objects to find...

Build confidence in proofs by proving a known property. Pupils explore two approaches to proving base angles of isosceles triangles are congruent: transformations and SAS. They then apply their understanding of the proof to more complex...

Can they put it all together? Ninth graders apply what they know about proofs and triangle congruence to complete these proofs. These proofs go beyond the basic triangle congruence proofs and use various properties, theorems, and...

Using patty paper, classes determine that only one triangle is possible when given two specific angle measures and a side length. As the 10th instructional activity in the series of 29, young math scholars add these criteria to those...

Looking to challenge your students that have mastered basic triangle congruence proofs? A collection of proofs employ previously learned definitions, theorems, and properties. Pupils draw on their past experiences with proofs to...

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.

Everyone knows that opposite sides of a parallelogram are congruent, but can you prove it? Challenge pupils to use triangle congruence to prove properties of quadrilaterals. Learners complete formal two-column proofs before moving on to...

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...

Starting with similar triangles and dilation factors, this unit quickly and thoroughly progresses into the world of right triangle features and trigonometric relationships. Presented in easy-to-attack modules with copious application...

Given a diagram of connected or overlapping triangles, individuals must find congruent parts using various properties. Pictures include reflexive sides and vertical angles amongst the marked congruent parts.

Construct an understanding of triangle congruence through a visual analysis. Young scholars find that given two sides and a non-included angle, sometimes two possible triangles are produced. Their analysis shows that if the non-included...

Building on the previous lesson in the 29-part series, the ninth lesson asks individuals to construct a triangle given specific criteria. First, they are given three specific side lengths, followed by two sides and the included angle....

A quadrilateral is drawn on the coordinate plane, and eighth grade geometers find the length of each side and the diagonals by applying the Pythagorean theorem. 

Determine whether two triangles are similar. The lesson presents opportunities for pupils to find the criterion needed to show that two triangles are similar. Scholars use the definition of similarity to find any missing side...

The Hopewell people of the central Ohio Valley used right triangles in the construction of earthworks. Pupils use the Pythagorean Theorem to determine missing dimensions of right triangles used by the Hopewell people. The assessment task...

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...

Prove the Law of Sines two ways. The ninth segment in a series of 16 introduces the Law of Sines to help the class find lengths of sides in oblique triangles. Pupils develop a proof of the Law of Sines by drawing an altitude and a second...

Trace the links between a variety of math concepts in this far-reaching unit. Ideas that seem very different on the outset (like the distance formula and rigid transformations) come together in very natural and logical ways. This...

Just what does it take to show two rhombuses are similar? The assessment task asks pupils to develop an argument to show that given quadrilaterals are rhombuses. Class members also use their knowledge of similar triangles to show two...

What figure is formed by connecting the midpoints of the sides of a quadrilateral? The geometry assessment task has class members work through the process of determining the figure inscribed in a quadrilateral. Pupils use geometric...

Under which conditions can a triangle be classified as isosceles? High schoolers practice identifying isosceles triangles and special line segments, including angle bisectors, medians of triangles, and perpendicular bisectors of sides of...

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...