Geometry

Lesson 3

Math

Unit 7

6th Grade

Lesson 3 of 17

Objective


Find the area of acute triangles using height and base.

Common Core Standards


Core Standards

  • 6.G.A.1 — Find the area of right triangles, other triangles, special quadrilaterals, and polygons by composing into rectangles or decomposing into triangles and other shapes; apply these techniques in the context of solving real-world and mathematical problems.

Criteria for Success


  1. Find the area of acute triangles by dividing them into two right triangles, finding the areas of the right triangles, and adding the areas.
  2. Understand that the line segment that represents the height of a triangle is always perpendicular to the line segment representing the base. 
  3. Determine that the formula $${A={1\over2}bh}$$ can be used with non-right triangles. 
  4. Identify and draw the line segment that represents the height of a triangle given a base.
  5. Find the area of acute triangles using base and height. 

Tips for Teachers


  • This is the second of three lessons on finding the area of triangles. In this lesson, students decompose acute triangles into right triangles to find area and determine that the formula to find the area of right triangles will also work for acute triangles (MP.7). 
  • Students continue to re-engage in 6.EE.2, evaluating the area of triangles using the formula.
  • Students will need to know the meaning of the word perpendicular in order to accurately understand how the base and height of a triangle are related. If needed, review this term. 

Lesson Materials

  • Optional: Index cards (1 per student)
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Anchor Problems

25-30 minutes


Problem 1

Two triangles are shown below with some measurements. 

a.   Find the area of Triangle A.

b.   Can you find the area of Triangle B with the measurements given? Why or why not?

c.   Triangle B is redrawn below. A new line has been drawn to divide Triangle B into two right triangles. Find the area of Triangle B in two different ways.

Guiding Questions

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Student Response

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Problem 2

In each triangle below, draw a line to represent the height of the triangle. Use an index card if helpful.

Guiding Questions

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Student Response

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References

Open Up Resources Grade 6 Unit 1 Lesson 10Lesson 10.2

Grade 6 Unit 1 Lesson 10 is made available by Open Up Resources under the CC BY 4.0 license. Copyright © 2017 Open Up Resources. Download for free at openupresources.org. Accessed March 20, 2018, 4:18 p.m..

Modified by Fishtank Learning, Inc.
Open Up Resources Grade 6 Unit 1 Lesson 10Summary

Grade 6 Unit 1 Lesson 10 is made available by Open Up Resources under the CC BY 4.0 license. Copyright © 2017 Open Up Resources. Download for free at openupresources.org. Accessed March 20, 2018, 4:18 p.m..

Problem 3

Which triangle has the greater area?

Guiding Questions

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Student Response

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Problem Set

15-20 minutes


Give your students more opportunities to practice the skills in this lesson with a downloadable problem set aligned to the daily objective.

Target Task

5-10 minutes


Identify a base and a corresponding height in the triangle below. Use them to find the area of the triangle.

Student Response

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References

Open Up Resources Grade 6 Unit 1 Lesson 99.4: Two More Triangles

Grade 6 Unit 1 Lesson 9 is made available by Open Up Resources under the CC BY 4.0 license. Copyright © 2017 Open Up Resources. Download for free at openupresources.org. Accessed March 16, 2018, 3:44 p.m..

Modified by Fishtank Learning, Inc.

Additional Practice


The following resources include problems and activities aligned to the objective of the lesson that can be used for additional practice or to create your own problem set.

  • Examples where students identify the height in acute triangles given different bases
  • Error analysis of triangles with incorrectly drawn heights

Next

Find the area of any triangle using height and base.

Lesson 4
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Lesson Map

A7CB09C2-D12F-4F55-80DB-37298FF0A765

Topic A: Area of Triangles, Quadrilaterals, and Polygons

Topic B: Polygons in the Coordinate Plane

Topic C: Volume of Rectangular Prisms

Topic D: Nets and Surface Area

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