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Lesson Plan
Shodor Education Foundation

Triangle Area

For Teachers 6th - 9th Standards
While the lesson plan 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...
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Interactive
CK-12 Foundation

Alternate Formula for the Area of a Triangle: Alternate Area of a Triangle

For Students 10th - 12th
It's always nice to have a plan B. Pupils investigate an alternate formula for the area of a triangle that uses sine. A set of challenge questions shows how the new formula relates to the well-known formula of (1/2)bh.
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Activity
Noyce Foundation

Lyle's Triangles

For Students K - 12th Standards
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....
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Lesson Plan
Curated OER

Finding the Area of an Equilateral Triangle

For Teachers 9th - 11th Standards
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...
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Lesson Plan
EngageNY

Perimeter and Area of Triangles in the Cartesian Plane

For Students 9th - 12th Standards
Pupils figure out how to be resourceful when tasked with finding the area of a triangle knowing nothing but its endpoints. Beginning by exploring and decomposing a triangle, learners find the perimeter and area of a triangle. They then...
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Activity
101 Questions

Best Triangle

For Teachers 9th - 12th Standards
What makes an equilateral triangle equilateral? It turns out it's much more than just the side lengths! Learners analyze four different triangles to determine the best equilateral triangle. They create a formula that they later use to...
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Lesson Plan
EngageNY

Using Trigonometry to Determine Area

For Students 9th - 10th Standards
What do you do when you don't think you have enough information? You look for another way to do the problem! Pupils combine what they know about finding the area of a triangle and trigonometry to determine triangle area when they don't...
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Activity
Curated OER

Unit Squares and Triangles

For Teachers 9th - 11th Standards
This is an interesting geometry problem. Given the figure, find the area of a triangle that is created by the intersecting lines. The solution requires one to use what he/she knows about coordinate geometry, as well as triangle and angle...
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Activity
5280 Math

Triangle Area Patterns

For Teachers 8th - 10th Standards
Combine algebraic and geometric strategies to find solutions. The task asks learners to find the coordinates of a third vertex of a triangle to create a triangle with a specific area. The project is a set of seven problems that helps...
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Activity
Curated OER

Triangle Series

For Teachers 9th - 12th Standards
Your algebra learners emphasize the"geometric" in geometric series as they use a common ratio between algebraic terms and find that it corresponds to a repeated similarity transformation. 
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Lesson Plan
EngageNY

Perimeter and Area of Polygonal Regions in the Cartesian Plane

For Students 9th - 12th Standards
How many sides does that polygon have? Building directly from lesson number eight in this series, learners now find the area and perimeter of any polygon on the coordinate plane. They decompose the polygons into triangles and use Green's...
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Activity
Education Development Center

Finding Triangle Vertices

For Teachers 6th - 7th Standards
Where in the world (or at least in the coordinate plane) is the third vertex? Given two coordinate points for the vertices of a triangle, individuals find the location of the third vertex. They read an account of fictional...
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Lesson Plan
EngageNY

Real-World Area Problems

For Students 7th Standards
Not all structures take the shape of a polygon. The 21st lesson in a series of 29 shows young mathematicians they can create polygons out of composite shapes. Once they deconstruct the structures, they find the area of the composite figure.
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Lesson Plan
Virginia Department of Education

Area and Perimeter

For Students 8th Standards
Develop a strategy for finding the area and perimeter of irregular figures. Building on an understanding of finding area and perimeter of rectangles and triangles, learners apply the same concepts to composite figures. After practicing...
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Lesson Plan
Curated OER

Volume and Surface Area

For Teachers 5th - 6th
Students explore volume and surface area. In this math instructional activity, students fill boxes with cubes to identify the volume of the boxes. Students discuss area.
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Lesson Plan
Curated OER

Concept Attainment Model: Volume and Surface Area

For Teachers 4th - 7th
Using a concept attainment approach, learners identify surface area and volume by sorting examples (photos) that depict each concept (positive)  from those that don't (negative). Then as a class, they develop definitions of each term...
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Lesson Plan
Curated OER

Triangle in the Matrix

For Teachers 9th - 12th Standards
Young mathematicians represent a triangle with a matrix and use the determinant to find the area of three given triangles. Learners also verify the formula for area of a triangle. 
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Assessment
Balanced Assessment

Triangle in Circle

For Students 6th - 8th
Even kindergartners can draw triangles in circles, but the assessment task requires a bit more geometric knowledge. Scholars investigate triangles that have a diameter of a circle as one of its sides. They must consider triangles that...
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Lesson Plan
Alabama Learning Exchange

Triangle Area: No Height? Use the Sine

For Students 9th - 12th Standards
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.
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Lesson Plan
EngageNY

Perimeter and Area of Polygonal Regions Defined by Systems of Inequalities

For Students 9th - 12th Standards
When algebra and geometry get together, good things happen! Given a system of inequalities that create a quadrilateral, learners graph and find vertices. They then use the vertices and Green's Theorem to find the area and perimeter of...
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Lesson Plan
Mathematics Assessment Project

Solving Problems with Circles and Triangles

For Teachers 9th - 12th Standards
After completing a task involving examining the ratio of areas of triangles and circles in a given figure, scholars examine sample responses to identify other strategies they could use to solve the problem.
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Assessment
Concord Consortium

Area Upgrade

For Students 10th - 12th Standards
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.
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Lesson Plan
Mathematics Assessment Project

Evaluating Statements About Length and Area

For Teachers 9th - 12th Standards
Class members complete an assessment task by identifying whether statements about triangles and quadrilaterals are always true, sometimes true, or never true. They then participate in a sorting activity with the same objective.
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Lesson Plan
Curated OER

Altitude, Median, and Angle Bisector of a Triangle

For Teachers 9th - 12th Standards
Learners investigate the special properties of an altitude, a median, and an angle bisector and explore how these special segments divide the area of a triangle. The dynamic nature of Cabri Jr. allows pupils to form and verify conjectures.

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