Warm ups 3-31-09What is the estimated perimeter of the shape?

10 cm

5cm

10 cm

C = π d 10For both blue parts together!!

They both form one whole circle!!

+ 20P=

Use 3.14 for pi!

Which formula could you use to determine the height of the triangle?

15

120h

15

120h

1

120

2

15

h

15 in

h

Area = 120 sq. in.

A.

B.

C.

D.

2

)120(15h

15

)120(2h

2

bhA120

15

1

15h = 240

15 15

15

240h

Two correct answers

What is the Area that is not covered by the pupil?

Iris

Pupil3 mm

5 mm

Area of circle notes

• Not the outer edge, the inside space• Multiply

or

or

RadiusRadius14.3

RadiusRadiusabout 3

2r

MOST COMMON MISTAKE!!DO NOT DO THIS!!!!

Question: the radius is 7 mm on a circle. What is the area?

Student does: A = 3 x 7 x 7 =

A = 3 x 14 =

A = 52

WHAT IS THE MISTAKE???

http://illuminations.nctm.org/ActivityDetail.aspx?ID=6

2rA