Area of Triangles and Rectangles

[Sharma]

Note: See attached document for all tasks and handouts

Materials:
1-inch square tiles (approx. 50 per student)
Scissors (1 per student)

Task 1
Pass out 1-inch square tiles and the packet of “grids” for each student. Ask students what “Area” is?
Have participants start on task 1, making sure that students use the tiles and that everyone in the groups has sketched a rectangle with different dimensions. When you see that the groups are close to finishing their first task, ask for volunteers to give their dimensions. Make a chart in the front of the room with their information, and lead the following discussion.

Have students use think-pair-share to discuss their responses to questions 1 and 2 and then call on students to share ideas.

Important Ideas for Class Discussion
• Why does a 3 x 2 make sense for the number of tiles, i.e. area? (because you have 3 groups/rows of 2, hence this is multiplication )
• So why does it make sense to have b x h as a representation of area? (because you have b groups of h; hence this is the definition for multiplication)

IMPORTANT: Point out that now they have a formula for finding the area of a RECTANGLE using the definition of multiplication. Have the students record their formula in the text box on their page.

Task 2
Notes
Have the students start the second task. Note that the students are to continue to use the square tiles to get an estimate of the area. They may compensate for the overlaps (i.e. only count half a square). When you see that the group is close to finishing their first task, lead the following discussion.

Class Discussion
• Of the three sides of the triangle, two of them are called legs and one is called the hypotenuse. Which two do you think are the legs and why? (the two that form a right angle)
• What type of triangle is this? (right triangle)
• How do we define the base and the height of a triangle?

Draw the following chart in the front of the room (make sure to get all estimates for Area and record all): (see attachment)

Source: http://auhsdmath.pbworks.com/

Attachments:

1. WhereDidThatFormulaComeFrom.doc
2. WhereDidThatFormulaComeGrids.doc

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