The Most Famous Ratio of All

Students develop the definition of a circle using diameter and radius. Students know that the distance around a circle is called the circumference and discover that the ratio of the circumference to the diameter of a circle is a special number called pi. Students know the formula for the circumference of a circle, of diameter, and radius. Although students were introduced to circles in kindergarten and worked with angles and arcs measures in Grades 4 and 5, they have not examined a precise definition of a circle.