Area of a Triangle

What is a triangle?All triangles are related to rectangles or parallelograms:

You can draw a diagonal line in any rectangle or parallelogram.

Each rectangle or parallelogram is made up of two triangles!

What is the Area of a Triangle?

The area formula for a rectangle or a parallelogram is: A = bh.

Each triangle is ½ of a rectangle or a parallelogram.

There are two triangles in these shapes!

The Formula!Remember the area formula for a rectangle or

parallelogram is A=bh and that each rectangle and parallelogram has TWO triangles in their shape.

Using this information to develop your own formula.

Can I have a drum roll please?!

Without further ado your formula should look something like…

The area formula for a triangle is

It can also be written as

bhA2

1

Finding the Area of a Triangle

Determine which measurement is the height:The height is inside the triangle

The height is outside the triangle

The height is a side of the triangle

Finding the Area of a Triangle

Pay close attention to the pictures below. You may notice that some of the triangles have been rotated or hidden in pictures.

Find base and height in these examples:

base = 10 cmheight = 9 cm

base = 12.1 mheight = 6.4 m

base = 7 ydheight = 4 yd

Applying the Area Formula

Write the area formula exactly as it appears on the FCAT Reference Sheet.

Rewrite the area formula substituting the values that you know.

Solve one step at a time rewriting after each step.

Applying the Area Formula

Example: Find the area of the triangle shown below.

A = ½ bh

A = ½ × 15.6 × 11.25

A = ½ × 175.5

A = 87.75 square

meters

Rally Coach1. Students sit in pairs.

2. First Problem: Partner A solves; Partner B coaches and praises.

3. Next Problem: Partner B solves; Partner A coaches and praises.

4. Continue solving problems.

Finding the Area of a Triangle

With your shoulder partner find the area of the following triangles using Rally Coach.

1.

2.

3.

4.

Finding the Area of a Triangle

With your shoulder partner find the area of the following triangles using Rally Coach.

1.

2.

3.

4.

Answer:90 cm2

Answer:45 cm2

Answer:425.25 mm2

Answer: 14 yd2

Check your Understanding

Find the area of the following two triangles independently.

6 ft.

3 ft.

7 cm.

5 cm.

9 mm.

4 mm.

11 km.

8 km.

Check your Understanding

Find the area of the following two triangles independently.

1) 9 ft2

2) 17.5 cm2

3) 18 mm2

4) 44 km2

Number Correct

4 I completely understand this skill, can do all problems on my own, and can help others learn.

3 I can do simpler problems on my own but need help to complete the complex problems.

2 I need help to complete all problems whether simple or complex.

0 – 1 I do not understand this concept even with help.

Check your Understanding

Finding the Area of a Triangle

From where and how did we derive the area of a triangle formula?

Exit QuestionIndependently find the area of the following triangle on a separate slip of paper. This will act as your exit ticket.