HL Triangle Congruence: Lesson

Use a triangle area formula that works when the height is unknown. The eighth installment in a 16-part series on trigonometry revisits the trigonometric triangle area formula that previously was shown to work with the acute triangles....

Is this enough to show the two triangles are congruent? Small groups work through different combinations of constructing triangles from congruent parts to determine which combinations create only congruent triangles. Participants use the...

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...

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 used this theorem to solve problems involving a right...

In this part 2 video, Sal finishes the trigonometric word problem of the wayward ship captain. He wisely continues the algebra work on the problem before finally turning to his calculator for the very last calculation.

With pen in hand and diagrams at the ready, Sal demonstrates problem-solving and test-taking skills in this informative video. Problems 7-9 involve inequalities, linear equations, and measuring angles in a right triangle.

Sal clarifies that doing a math problem the correct way isn't really the correct way to do it on the SAT. If students find this statement confusing, they will understand Sal's point after watching him work quickly and efficiently through...

It is special—given one length, you can find the other two. A segment of a basic geometry playlist provides the ratio of the lengths of sides of a 30-60 right triangle. The presentation shows how to use the ratio to find side lengths...

Triangles are classified by their angle measurement as well as by the length of their sides. Here are some names that identify the types of triangles: right, isosceles, equilateral, scalene, obtuse, and acute. Watch this video to learn...

While the activity 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...