Digital Skills: Developing Online Assessment Skills in Everyday Classroom Activities Western Reserve Public Media
Area of a Triangle
Discovering the formula for the area of a triangle
I can:

I can determine the area of a rectangle and the area of a triangle.

Tech Skills:
  • Online Ruler

  • Manipulating a digital graph

  • Digital Table

Materials and Resources:

Math Playground Perimeter and Area

Math Playground Geoboard

Math Warehouse - Triangle Area using area formula

NCTM Area Tool

Grade Level:
  • 6th Grade

Subject Area:
  • Mathematics


Activity 1

Students should warm-up by working through some rectangle perimeter and area problems using the Math Playground Area and Perimeter interactive. Students should successfully complete the twelve problems before moving on to the area of a triangle portion of the lesson.

Have students open the Math Playground digital geoboard (this interactive requires Flash Player so you must use Firefox, Internet Explorer or Safari to view - not Chrome). Allow them a short time to click and read the instructions, play with the bands and make some shapes. Demonstrate the following problem for the students before having them begin partner work. Create the rectangle below:


Measure the rectangle by clicking on the measure button.



Create a triangle inside the rectangle, to demonstrate the relationship between the area of a rectangle and a triangle. Be sure to select a color for the triangle shape and click the measure button to show the area of the triangle.

Demonstrate other possible triangles and measure their areas.


If necessary demonstrate the entire process again creating a different rectangle.

Have students create their own rectangle, measure the area and record it on paper. Follow with the triangle as demonstrated and record. Students should repeat this process three times and note any patterns or their observations. Students should observe that triangle’s area is half of the rectangle’s area. If students need to input more than three entries into their table to see the pattern they should be permitted to do so. Students should see that the area of a triangle is ½(bxh).



Activity 2

Using the area tool from NCTM have students investigate the area of a triangle with a different tool (this interactive requires Flash Player so you must use Firefox, Internet Explorer or Safari to view - not Chrome). Students will create a digital table. Students are able to select whole number segment lengths but will need to manipulate the points on the interactive to do so. Ask students questions to deepen their understanding. What happens to the area when the height of the triangle is doubled? What happens when the height is tripled? If the base of the triangle is doubled?


Practice Activity

Have students complete the practice problems on the Math Warehouse, using the formula.


6.G.1 Through composition into rectangles or decomposition into triangles, find the area of right triangles, other triangles, special quadrilaterals, and polygons; apply these techniques in the context of solving real-world and mathematical problems

Supplementary Resources:

Additional Triangle Area Interactive - Demonstrates the number of square units “inside”.


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