AB: optional BC: required

MB: optional ON: required

Teacher Resource 6.2 Unit 13 Measurement pp. P-24–27

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ME6-12

Area of Triangles

Students will:

• develop the formula for the area of a triangle, using the area of a rectangle, and then apply it.

AP Book 6.2 pp. 106–107

Say the area of the rectangle was 300 cm².

What is the area of each triangle?

See p. P-24 for details.

Hint: The rectangle has the same length and width (or width and height) as the sides of the triangle that meet at the right angle.

Have students copy these triangles onto grid paper.

Then draw a rectangle around each right triangle. See pp. P-24–25 for details.

We can split each of these triangles into two right triangles to find their area.

Area of rectangle = width of rectangle × height of rectangle

Next, replace "area of rectangle" with the formula. Continue until you get to the short form of the area of triangle formula.

See p. P-25 for details.

We know that …

Short Form of Formula:

Bonus:

Two different triangles with area 15 square units

c) 18 square units

b) 16 square units

a) 12 square units

Exercises:

On grid paper, make a triangle with the given area.