Pi is the ratio of a circle's circumference to its diameter. The symbol π represents pi in Greek letters. Pi is also known as Archimedes' constant
Cycloid is a curve formed by a fixed point rolling on a circle without slipping. First studied by Galileo in 1599. Repeats shape after each cycle with repeating length of 2πr
Radius is the distance from center to perimeter of a circle or sphere. Name comes from Latin "radius" meaning ray or chariot wheel spoke. Diameter is twice the radius
Arc length is the distance between two endpoints of a circle's arc. Formula: arc length = 2πr × (central angle/360). Central angle must be in degrees or radians
Draw crossed lines inside circle to pinpoint center. Create overlapping circles to find exact center. Draw square around circle and find center at intersection
Diameter equals twice the radius (radius is distance from center to edge). Diameter equals circumference divided by pi (circumference divided by π). Diameter equals square root of area divided by pi multiplied by 2