Published on February 14, 2014
What is a circle? : What is a circle? By Humera Shaikh The Definition : The Definition A circle is a round, two-dimensional shape. It has a middle point (center). All of the points that make the curved line of the shape are equidistant from that point. Equidistant means “having an equal distance” We see circles everyday… : We see circles everyday… …when we use money! …when we tell time! …when we go on a vacation! …when we go for a ride! How do you draw a circle? : How do you draw a circle? Use a math compass: Lines inside a circle : Lines inside a circle There are many lines inside a circle. Any line that touches two points on the circle is called a chord. Any line that touches two points on the circle and goes directly through the center is called a diameter. Any line that begins at the center and touches one point on the circle is the radius. The radius is one-half the length of the diameter. radius diameter chord Circle Measurements: Circumference : Circle Measurements: Circumference We use the diameter and radius to measure the area and circumference of a circle. The circumference is the distance around a circle. (You may think of this as the circle’s perimeter.) To measure the circumference, multiply the diameter by the number, π (Pi). π is equal to 3.14159265... We commonly use 3.14 to find an estimate answer. diameter = 2 cm Example: circumference = dπ dπ = 2(3.14) circumference = 6.28 cm Circumference = 6.28 cm Circle Measurements: Area : Circle Measurements: Area To find the area of a circle, you must know the radius or the diameter of the circle. If you know the diameter, divide that number by 2 (this will give you the radius). Area = πr² Example: area = πr² πr² = (3.14)(3)² area = 3.14(9) area = 28.26 ft² Radius = 3 ft There are 28.26 squares inside this circle! More circle parts… : More circle parts… tangent line arc sector segment What did you learn about circles? : What did you learn about circles?