Warm Up

1. What is the perimeter of a square with side lengths of 15 in.?

2. What is the perimeter of a rectangle with length 16 cm and width 11 cm?

60 in.

54 cm

The perimeter of a figure is the distance around it. To find the perimeter you can add the lengths of the sides.

Additional Example 1: Finding the Perimeter of a Polygon

Find the perimeter of the figure.

2.8 + 3.6 + 3.5 + 3 + 4.3

Add all the side lengths.

The perimeter is 17.2 in.

Try This: Example 1

Find the perimeter of the figure.

3.3 + 3.3 + 4.2 + 4.2 + 3

Add all the side lengths.3.3 in. 3.3 in.

4.2 in.4.2 in.

3 in.

The perimeter is 18 in.

Additional Example 2: Using a Formula to Find Perimeter

Find the perimeter P of the rectangle.

P = 2l+ 2w

Substitute 12 for l and 3 for w.P = (2 • 12) + (2 • 3)

P = 24 + 6

P = 30

Multiply.

Add.

The perimeter is 30 cm.

12 cm

3 cm

How many individual boxes are there here?

1 2 3 4 5 6 7

2

3

4

5

6

7

Learn to find the area of rectangles, triangles, and parallelograms.

Vocabulary

area

Insert Lesson Title Here

The area of a figure is the amount of surface it covers. We measure area in square

units.

Additional Example 2: Estimating the Area of a Rectangle

Find the area of the figure.

Write the formula.

Substitute 15 for l.Substitute 9 for w.

A = lw

A = 15 • 9

A = 135

The area is 135 in2.

15 in.

9 in.

Try This: Example 2

Find the area of the figure.

Write the formula.

Substitute 13 for l.Substitute 7 for w.

A = lw

A = 13 • 7

A = 91

The area is 91 in2.

13 in.

7 in.

46 ft.

3 ft.

46 ft.

3 ft.

25 cm.

5 cm.

You can use the formula for the area of a rectangle to write a formula for the area of a parallelogram. Imagine cutting off the triangle drawn in the parallelogram and sliding it to the right to form a rectangle.

The area of a parallelogram = bh. The area of a rectangle = lw.

The base of the parallelogram is the length of the rectangle. The height of the parallelogram is the width of the rectangle.

Additional Example 3: Finding the Area of a Parallelogram

Find the area of the parallelogram.

Write the formula.

Multiply.

A = bh

2 ft12

A = 2 • 112__ 1

4__ Substitute 2 for b

and 1 for h.

12__

14__

A = •52__ 5

4__

A = or 325 8

___ 18__

The area is 3 ft2. 18__

14

1 ft

Try This: Example 3

Find the area of the parallelogram.

Write the formula.

Multiply.

A = bh

A = 1 • 312__ 1

2__ Substitute 1 for b

and 3 for h.

12__

12__

A = •32__ 7

2__

A = or 521 4

___ 14__

The area is 5 ft2.14__

11 ft2

13 ft2

I made a DELICIOUS peanut butter and jelly sandwich for lunch today. I’m so excited to eat it!!! Dylan came to me crying and said he forgot his lunch! Since I’m so

nice, I cut my sandwich diagonally and gave one piece to Dylan and kept one for myself. Who got more

of the sandwich??

You can make a square out of two congruent triangles.

If the area of a triangle is HALF the area of the rectangle, what could we use for

the formula of a triangle?

New Formula

We can pretend the triangle is a rectangle and find the area of the rectangle! Then divide it by two.

LW ÷ 2

New Formula

We can pretend the triangle is a rectangle and find the area of the rectangle! Then divide it by two.

Additional Example 4: Finding the Area of a Triangle

Find the area of the triangle.

Write the formula.

Substitute 9.6 for b. Substitute 2.9 for h.

Multiply.

The area is 13.92 cm2.

A = 13.92

A = bh12__

A = (9.6 • 2.9)12__

A = (27.84)12__

Try This: Example 4

Find the area of the triangle.

Write the formula.

Substitute 8.5 for b. Substitute 3.4 for h.

Multiply.

The area is 14.45 cm2.

3.4 cm

8.5 cm

A = 14.45

A = bh12__

A = (8.5 • 3.4)12__

A = (28.9)12__

Lesson Quiz

Find the area of each figure.

1. 2.

3. What is the area of a parallelogram with base

16 in. and height 10 in.?

4. What is the area of a triangle with base 10 in.

and height 7 in.?

Insert Lesson Title Here

4.5 m

9.2 m41.4 m2 24 ft2

160 in2

35 in2