You will learn to find the perimeter and area for different shapes and the circumference of circles.

s w s l

h r b s P = s C = 2  r = A =  r 2

2

1 + s  d 2 + s

s+s+s+s

l+w+l+w 3 A = lw

What is a perimeter?

• Perimeter is the distance all the way around an object.

• The perimeter of a circle is called the circumference .

How To Find Perimeter  Find the length of each side of the object.  Add all the lengths of the sides together.

 This total is the perimeter.

Lets’ find the perimeter.

8 + 4 + 8 + 4 = 24.

This rectangle has a perimeter of 24.

How about this perimeter ?

6 + 5 + 5 + 6 + 12 = 34.

This pentagon has a perimeter of 34.

Now lets’ try a circumference: • c=2πr or c=πd • r = radius (half the distance across a circle) • d = diameter (the distance across a circle) • Note that 2r = d

Now lets’ try a circumference: Find the circumference of a circle with a diameter of 12 cm.

c = πd • c = π  12 • c = 3.14•12 • c = 37.68 cm 12 cm

Lets’ try aother circumference: Find the circumference of a circle with a radius of 3 meters.

• c = 2πr • c = 2  π  3 • c = 2 • 3.14 • 3 • c = 18.84 m 3 m

What if we know the circumference ?

If the circumference of a circle is approximately 50.3 cm, find the radius. (Use 3.14 for π) C = 2 •π•r 50.3 = 6.28r

50.3

/ 6.28

= r 8 cm  r

Time for area.

4 cm • • • •

Area of a rectangle A = bh A = 4(2) A = 8 cm ²

2 cm

Not done yet!!

6 mm 7 mm • Area of a triangle: • A = ½ bh • A = ½ (6)(7) • A = 21 mm²

What if you are missing aside ?

If the base is 16, and the area is 40, what is the height?

A = ½ bh 40 = ½

H = ?

40/8 = h 5 in = h 16 in

Here comes the area of a trapezoid b 2 = 10 ft 5 ft b 1 = 6 ft • A = ½ (b 1 +b 2 )h • A = ½ (6 + 10)(5) • A = ½(16)(5) • A = 40 ft²

And yet, here’s another area of a trapezoid 12 km 3 km 8 km • A = ½ (8 + 12)(3) • A = ½ (20)(3) • A = 30 km²

Let’s find a missing side 8 km If the area of the 4 km trapezoid is 24, and the height is 4 and base 1 B 2 = ? km A = ½ (h)(b 1 + b 24 = ½ (4)(8 + x) 2 ) is 8, what is the other base?

24 = 2(8 + x) 24 = 16 + 2x 24 – 16 = 2x 8 = 2x 4 km = x

Just one more, the area of a circle

10 m

• A = πr² • A = 3.14(10)² • A = 3.14(100) • A = 314 m²

OK, one last area of a circle.

8 in • Diameter = 8 in • Radius = 4 in • A = 3.14(4)² • A = 3.14(16) • A = 50.24 in²

Assignment

Geometry

1.9 Perimeter, Circumference, and Area

Find the perimeter and area of each rectangle. Label each measurement.

3 in 6 in 1.

Find the missing measure in each formula if P = 2l + 2w and A = lw.

2.

1 yd 4. l = 4.5, w = 1.5, P = ?

5. l = 2.2, w = 1.1, A = ?

6. l = 12, A = 30, w = ?

7. A = 3 ½, w = ½, l = ?

8. P = 13, w = 2.5, l = ?

12 yd Find the circumference and area of each circle. Label each measurement.

9.

15 cm

3.

1.65 cm 10.

3 m

1.65 cm