Lesson: Area of Triangles

Area of Triangles

Objective: Find the area of triangles

Math Response

WARM-UP: What is the area of the parallelogram above?

Type answer here

Correct Answer: 40

Deg^°

Rad

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)

Math Response

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?

Type answer here

Correct Answer: 15

Deg^°

Rad

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

​What is the area of this triangle?

Math Response

Find the area:

Type answer here

Correct Answer: 40

Deg^°

Rad

Multiple Choice

Which side is the base?

• 18 cm

• 14 cm

• 8 cm

• 6 cm

Multiple Choice

Which measurement is the height?

• 3 in

• 4 in

• 12 in

• 15 in

Math Response

What is the area of the triangle?

Type answer here

Correct Answer: 38.5

Deg^°

Rad