Show your school spirit while proving theorems about triangles! Your student geometers are charged with coming up with a new design for the school pennant, following specific guidelines. Along the way, they need to prove the theorem that base angles of an isosceles triangle are congruent. Not only is this a learning activity, if you allow time to decorate the pennants, you'll end up with great room or hall decorations. 
Delving into basic trigonometry, this resource shows how to find the area of an inscribed equilateral triangle. Using a high-level problem, HeronÕs theorem is used to find the area of a figure. Prior to SAT testing, use this as a review.
As the fourth part of a series on the Pythagorean Theorem, Sal continues an exploration of the ways to calculate the length of sides of a right triangle using algebra. He also explores using this theorem to solve problems involving a right triangle with 30 degree and 60 degree angles.
Although a rather complicated topic, this video manages to clearly explain the concept of solving problems involving similar triangles. It employs problem solving to determine whether two figures are similar triangles. In addition, it provides guidance for finding the anglesÕ values. Tip: the presentation finishes prior to solving the final problem. Furthermore, this is the first part of a series on similar triangles.
The process for calculating values using a right triangle with angles of 45 degrees is covered in this third portion of the Pythagorean Theorem series. Here, Sal uses algebra to calculate the value of an angle. The solution to the sample problems involves a complicated resolution. As a result, it would be helpful in preparing for the SAT.
Finding the area of each of the triangles that are created by drawing two diagonal lines through a rectangle is explored in this lecture. It provides a detailed explanation of how to use a formula to solve the given problem. Tip: Use this for test preparation purposes.
Building on concepts in the first part of the series on similar triangles, installment number two explores how to find the values for given angles in a triangle. These problems are solved by using algebra and ratios. A step-by-step explanation simplifies the process of solving these rather complicated problems.
After addressing the terminology used with medians and centroids of triangles in the first part of this series, the instructor shows how to solve this type of problem. He illustrates the concepts by using a high-level problem. Consequently, it will likely reinforce comprehension of algebraic expressions.
Using this video, which is the fourth in a series, the instructor continues a discussion involving the Pythagorean theorem. This video focuses on calculations involving right triangles with 30 and 60 degree angles.
Most high schoolers are very familiar with the area of the triangle being equal to 1/2 base times the height. Here, they will develop and test their formula for the area of a triangle when given two adjacent sides and the included angle. After they develop their formula, they will use a dynamic geometry software system, such as Geometer's Sketchpad or GeoGebra to test their conjecture. 
Geometry juniors apply the Pythagorean theorem to two triangles to determine a final calculation. 
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.
Your geometry learners will use dynamic geometry software to find the centroid of a triangle. Then they will play a game to find the balancing point of a triangle and compare it to the centroid.. 
Here the focus is on triangle congruence. Through an activity that requires investigation, questioning, and working together, geometers learn to identify corresponding parts of triangles to determine if the triangles are congruent. Triangles are transformed through reflection, rotation, and translation. 
Explore, investigate, and finally prove the angles in a triangle have a sum of 180 degrees. Young geometers use the Interior Angles Theorem, and properties and definitions of congruency. 
The problem seems simple: find the area of the equilateral triangle whose sides are each length 1. In fact, this same problem is solved in 8th grade, addressing a different Common Core standard, using the formula for area of a triangle to solve. Here the objective is to get geometry learners develop an understanding of two new solutions. One using congruent triangles, and the other using trigonometric ratios. 
While the lesson focuses on right triangles, this activity offers a great way to practice the area of all triangles through an interactive webpage. The activity begins with the class taking a square paper and cutting in in half; can they relate the area of the square to the right triangles? Then they use the webpage, which provides different triangles on a coordinate grid to calculate the the area. The lesson discusses right triangles, while medium and hard levels of the activity have non-right triangle examples. Learners should be able to find the area of a triangle when height or base is not obvious using the distance formula or box method if using the hard level examples. 
Looking for a nice activity that will help deepen your geometry learners' understanding of similar triangles? This activity maps a number of triangles embedded in a square on dot graph paper. Young geometers need to find as many different similar triangle pairs as they can find and justify their solutions. 
What can symmetry tell us about triangles? After looking at four examples, learners will come to realize that lines of symmetry are different for equilateral, isosceles, and scalene triangles. Use this guided practice activity as an introduction to classifying triangles based on their side lengths.
Two triangles are displayed on a coordinate plane. Youngsters apply a reflection and a translation to demonstrate their congruence. This exercise makes a terrific tool for teaching these concepts, or a way to assess learning.