Are two angles enough? Given two triangles, the class determines through the definition of similarity and transformations whether the two triangles are similar. Provided with pairs of triangles and measurements, small groups find out...

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. 

This amazingly extensive unit covers a wealth of geometric ground, ranging from constructions to angle properties, triangle theorems, rigid transformations, and fundamentals of formal proofs.  Each of the almost-forty lessons is broken...

Middle and high schoolers construct a triangle using Cabri Jr. They construct squares on each of the legs and hypotenuse of the triangle. Pupils show that the area of the squares on the leg equal the area of the square on the hypotenuse.

Why do people have scientific theories but not scientific facts? A quick video presentation defines scientific theory and the components necessary for developing a theory. The presenter emphasizes the difference between scientific proof...

Proofs do not exist only in geometry. The video shows the class different ways that proofs appear in algebra. Pupils work through a variety of algebraic proofs involving the divisibility of an algebraic expression or whether it is even...

It's just not enough to know that something is true. Part of a MVP Geometry unit teaches young mathematicians how to write flow proofs and two-column proofs for conjectures involving lines, angles, and triangles.

Construct yourself a winning geometry unit. A set of lessons introduces geometry scholars to constructions and proofs with compasses and straightedges. It also covers triangle congruence through transformations. This is the second of...

Imagine a world built of triangles. A performance task asks scholars to consider just that. They use their knowledge of special segments of a triangle to make decisions about the area of triangular plots of land.

Properly organize parallelograms. Given special parallelograms, the narrator of a short video explains the properties of each. The section of a playlist on geometry uses the properties to classify the special parallelograms.

No height? No problem! Learners use their knowledge and a little help from GeoGebra to develop the Law of Sines formula. The Law of Sines helps to determine the height of triangles to calculate the area.

The first five are red, so they all must be red, right? As part of a larger playlist on basic geometry, the video walks through an example of a conjecture and counterexamples by using a scenario of pulling candy out of a bag.

Teach budding mathematicians how to square a triangle with an interactive that shows a graphical proof of the Pythagorean Theorem. Pupils alter the lengths of the legs using sliders. Using the inputted lengths, the applet displays the...

No geometry class is complete without a proof. A short video in the Socratica Geometry playlist covers an algebraic proof of the Pythagorean Theorem. Simplifying an equation with two equivalent expressions for the area of a square leads...

See how parallelograms can produce congruent triangles. Given a diagram of a parallelogram, scholars must show that two triangles are congruent. The triangles are made from the diagonals of the parallelogram.

Don't just go halfway; use the entire resource. Given a triangle in the coordinate plane, young mathematicians show that a midsegment through two sides is parallel to the third side and half the length of the third side. This proves the...

Parallel lines through triangles result in a special proportion. Scholars prove the triangle proportionality theorem in a great lesson. The resource makes use of angle relationships and the similarity criteria to build on their geometry...

Cut straight to the proof. Given cutouts of different quadrilaterals, pupils draw diagonals. Learners cut up the figures along the diagonals to see whether they bisect each other. Scholars develop a geometric proof for the property they...

There is more than one way to prove the Pythagorean Theorem. Euclid and Einstein found the same way to prove the Pythagorean Theorem. The video introduces several other ways to prove the theorem along with the history of its use.

From any angle, the resource on proving angle relationships is a good one to use. Scholars first engage in activities that enable them to identify types of angles when a transversal cuts two parallel lines. In groups, they prove a...

Take the time to prove what seems obvious. The resource provides pupils a figure of a rectangle, which they use to develop a proof showing that the rectangle is also a parallelogram. Scholars must rely on the definition of a rectangle to...

Transform a diagram into a proof. Given two triangles on a coordinate plane, pupils develop a proof to show they are similar. The learners use the fact that two angles of one triangle are congruent to two angles of another and their...

What do congruent triangles have to do with diagonals of a rhombus? Given a rhombus, pupils develop a proof showing that a diagonal bisects opposite angles. The learners use what they know about congruent triangles to create the...

Move linearly from specific proofs to general proofs. Pupils use two proofs to show that linear functions grow by equal differences over equal intervals. The first proof uses a specific linear function and intervals. Using the process of...