DO NOWHomework:

– Perimeter, area & circumference Day 1 Wkst

– Midterms next Tuesday & Wednesday

•Warm-Up: What formulas do you remember for perimeter, area or circumference? Write as many as you can remember

MARCH 17, 2014

Today’s Lesson: Perimeter, Area, &

Circumference

Think about it…

• What is perimeter?–PeRIMeter: The distance around a

figure.

Area of a triangle

5cm

3cm

4cm

A = 1/2bh = 1/2(4)(3) = 6cm2

bhA2

1

Do you rememberthe formula?

What is the perimeter of the triangle?

Area of a rectangle

A = bh = 4x2 = 8in2

lwA

bhA

Do you rememberthe formula?

What is the perimeter of the

rectangle?

Area of a square

• A = bh = 3x3 = 9in2

lwA

bhA

sA

2

Do you rememberthe formula?

What is the perimeter of the square?

Area of a parallelogram

7 cm

Area = bh = (7)(4) = 28 cm2

Perimeter = 5 + 5 + 7 + 7 = 24cm

h = 4 cm5cm

bhA

Do you rememberthe formula?

Area of a trapezoid

10 cm

5 cm

hbb

A

2

21

h = 4 cm

23051042

1cmA

Do you rememberthe formula?

What about pi?(used when we talk about circles)

• What approximate number do we often use for pi?– 3.14– Pi is really a

nonterminating decimal that starts as 3.14159…

Area of a circle

2rA

Do you rememberthe formula?

56.12422 A

Do you remember?

• What is the special word that refers to the perimeter of a circle?

Circumference

• Formula:

• What does the d stand for?– Diameter!

• Diameter is the distance across the circle

– What if you don’t know the diameter?• If you know the radius, you can double it!

– The radius is the distance halfway across the object

dC

Circumference of a circle

dC

56.124 C

HINT!!

• What is a good strategy to use when doing problems that involve perimeter, circumference, or area?– Draw a picture!

You Try

• 1. Mr. Bill’s back yard is in the shape of a rectangle. It took him 600 feet of fence to enclose in his back yard. If the length of the yard is twice as long as the width, what are the dimensions of Mr. Bill’s yard?

#1 - Answer

• length = 200 feet

• width = 100 feet

You Try

• 2. A bicycle tire has a diameter of 24 inches. How far does the bike travel, in inches, when the tire completes 1 revolution?

#2 - Answer

• 75.36 inches

Think about it…

• What is area?– Area: The measure of the region that is

inside a closed plane figure.

You Try

• 3. A package containing a swivel stake and a 10-foot dog chain claims that it gives the dog more room to play than a 10-foot square pen. Is this a true statement and if so, how much more room does it allow the dog to play?

#3 - Answer

• circle = 314 ft2

• rectangle = 100 ft2

• Yes, difference = 214 ft2.

You Try

• 4. Mr. Santiago bought a rug with an area of 2500 square inches. Will the rug fit in the front hall, which is 48 inches by 60 inches?

#4 - Answer

• The area of the hall is 2880 ft2 so it will fit if the dimensions match okay. If the rug is 50 by 50, it will not fit.

Composite Figures

• You may have to look at the individual areas then add or subtract to find the answer.

• What is the area of the “dark blue” region?

8cm

16 cm

8 cm

6 cm

What is the area of the “dark blue” region?

• Area blue = Area of Rectangle – Area of Triangle = (8 x 16) – (½ x 8 x 6) = 128 – 24 = 104 cm2

8cm

16 cm

6 cm

8cm

Composite Figures

Find the area of this polygon

10 cm

5 cm

2 cm6 cm

Graph and find the area

Connections to EOG Assessment:

• A square room with an area of 324 square feet is tiled using square tiles with a side length of 1 foot.  How many tiles line each wall of the room?

• A)  17 • B)  18• C)  19• D)  20