Area of Triangles

Area of Triangles

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AREA REVIEW

Area: The number of square units (units²) it takes to cover the surface of a figure.

In the picture to the right, we would just count the squares.

The rectangle and square are easy.

The TRIANGLE presents a challenge

Poll

If you had to estimate how many squares were in the triangle, what would be your estimate?

• 15 squares

• 13 squares

• 14 squares

• 16 squares

• 17 squares

Area of a Triangle

(1) Made a copy of the triangle

(2) I flipped the copy

(3) Slid the copy over and now we have a parallelogram.

Area of a Triangle

Area of a Parallelogram

A = bh

(4) Count to find the base

(6 squares)

(5) Count to find the height

(5 squares)

(6) Find the area of the parallelogram. (30 squares)

Fill in the Blank

Now we know the parallelogram has an area of 30 units.

Since we made the parallelogram from two triangles that were the EXACT SAME SIZE, how many squares would be in the red triangle?

ANSWER

The whole thing was 30 squares.

So...both triangles have to be 15 squares each.

Or the area of the triangle was the area of the parallelogram divided by 2.

30 ÷ 2 = 15

Area of a Triangle

Example 1

Fill in the Blank

What is the area of this triangle?

Fill in the Blank

What is the area of this triangle?

Multiple Choice

Which side is the base?

• 18 cm

• 14 cm

• 8 cm

• 6 cm

Multiple Choice

Which side is the height?

• 18 cm

• 14 cm

• 8 cm

• 6 cm

Multiple Choice

What is the area of the triangle?

• 108 cm²

• 54 cm²

• 48 cm²

• 24 cm²

Multiple Choice

What is the area of the triangle?

Remember: Base x Height ÷ 2

• 20 in²

• 12 in²

• 6 in²

• 10 in²

Open Ended

How do you find area of a triangle?