EngageNY
The Angle-Angle (AA) Criterion for Two Triangles to Be Similar
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...
Everyday Mathematics
Mathematics Within: Slope and Triangles
Learners discover a method for determining the slope of a line by creating and comparing similar triangles. They fold coordinate grids to make three similar triangles then measure the sides to compare the relationships between the...
EngageNY
Congruence Criteria for Triangles—ASA and SSS
How do you know if a pair of triangles are congruent? Use the lesson to help class members become comfortable identifying the congruence criteria. They begin with an exploration of ASA and SSS criteria through transformations and...
Illustrative Mathematics
Similar Triangles
Proving triangles are similar is often an exercise in applying one of the many theorems young geometers memorize, like the AA similarity criteria. But proving that the criteria themselves are valid from basic principles is a great...
Noyce Foundation
Lyle's Triangles
Try five problems on triangles. Levels A and B focus on shapes that can be created from right triangles. Level C touches upon the relationship between the area of a six-pointed star and the area of each triangle of which it is composed....
CK-12 Foundation
Pythagorean Theorem for Solving Right Triangles: Solving the Triangle
Observe the change in the trigonometric ratios as angles vary. An interactive provides the values of trigonometric ratios for both acute angles in a right triangle. Pupils create a right triangle to match given criteria and find the...
Illustrative Mathematics
Equal Area Triangles on the Same Base II
A deceptively simple question setup leads to a number of attack methods and a surprisingly sophisticated solution set in this open-ended problem. Young geometers of different strengths can go about defining the solutions graphically,...
Illustrative Mathematics
Extensions, Bisections and Dissections in a Rectangle
Gaining practice in translating a verbal description into a diagram and then an equation is the real point of this similar triangles exercise. Once the diagram is drawn, multiple methods are provided to reach the conclusion. An effective...
Illustrative Mathematics
Two Wheels and a Belt
Geometry gets an engineering treatment in an exercise involving a belt wrapped around two wheels of different dimensions. Along with the wheels, this belt problem connects concepts of right triangles, tangent lines, arc length, and...
Math Stars
Math Stars: a Problem-Solving Newsletter Grade 7
Put on your thinking caps because middle school math has never been more interesting in this huge resource full of thought provoking questions. Written as a newsletter, the resource has 10 two-page newsletters with a variety of...
Mt. San Antonio Collage
Properties of a Parallelogram
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...
Curated OER
What are the Kinds of Triangles?
Fifth graders classify triangles. For this triangle lesson, 5th graders learn about the characteristics that make up a triangle. They are instructed through video, PowerPoint slides, and teacher-led demonstrations.
Curated OER
Learning About Triangles
Upper graders label four triangles and fill in the labels correctly. They draw three original triangles and answer the questions about them.
Curated OER
The Centroid of a Triangle
Students familiarize themselves with the construct and measure menus. They demonstrate how to use the Sketchpad Calculator. They draw a triangle and construct the centroid. They shade in each of the small triangles and measure the area.
Curated OER
Area of Triangle
In this area of a triangle worksheet, students solve 3 problems where they calculate the area of a triangle when they are given the length of the base and the height and the formula.
Curated OER
Finding the Area of a Triangle
Fifth graders investigate the area of a triangle. In this geometry lesson, 5th graders practice finding the area of a triangle using the correct formula: 1/2bh.
Curated OER
Easy Worksheet: Area of Triangles
In this area of a triangle worksheet, students solve 6 graphing problems. Students find the area of a triangle given the three coordinates of the vertices.
Curated OER
A Triangle Expansion
Students review the foil method used to multiply two binomials. In this lesson on evaluating algebraic expressions, students are able to identify the coefficient in an algebraic expression, "act out" the foil method of multiplying...
Concord Consortium
Always, Sometimes, Never
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...
Curated OER
Amazing Triangles
Student scientists investigate triangle structures. In this building lesson plan, learners explore how to design triangle braces in the construction of structures in order to build a stronger base.
EngageNY
Solve for Unknown Angles—Angles in a Triangle
Assist your class with each angle of geometry as they use exterior angles to form linear pairs with adjacent interior angles. They cover multiple vocabulary terms and work practice problems, complete with justifications, before...
EngageNY
Identical Triangles
Explore vocabulary and notation related to triangles and congruence. The fifth instructional activity in the 29-part series helps pupils build their knowledge of triangle relationships. Individuals identify corresponding parts of...
EngageNY
Unique Triangles—Two Sides and a Non-Included Angle
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...
EngageNY
Checking for Identical Triangles
Examine an assortment of triangle congruence criteria in a single instructional activity. Building on the four previous lessons of the series, the 13th installment provides a mixture of the different triangle congruence criteria for...
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