CIRCLES

finding the circumference or the area

of a circle is an easy thing to do!

You just need to know a few simple terms!

First-- center Circle O A point in the exact middle of a circle—equal distances from all sides—used to name the circle.

Second-- diameter d=ab A line segment whose ends touch the edge of the circle and goes through the center. 1 diameter = 2 radii

Third-- radius (radii) r=ao, bo, od A line segment that goes from the center of a circle to the edge. 2 radii = 1 diameter or ½ diameter = 1 radii

Fifth-- d pi a b o h pi = 3.14 or 22/7 g the ratio of the diameter to the circumference of a circle. It has a value of about 3.14 or 22/7.

Fifth-- d pi a b o h pi = 3.14 or 22/7 g the ratio of the diameter to the circumference of a circle. It has a value of about 3.14 or 22/7.

circumference = pi times diameter Now for the work! circumference C = d This means circumference = pi times diameter The answer is in units.

Now for the work! circumference C = d C = 3.14 x 20 cm C~ 62.8 cm Remember—it is about equal because 3.14 is not the complete value of pi.

Multiply the radius by 2 to get the diameter! circumference C = d What if they only give you the value of the radius??? Multiply the radius by 2 to get the diameter! 16 cm C = 3.14 x (16 cm x 2) C~ 100.48 cm

Area A = r 2 Which means pi times radius times radius. 10 cm Remember—it is about equal because 3.14 is not the complete value of pi.