The value of pi is a special number based in geometry and used in trigonometry for the study of triangles and circles. Its discovery is historically attributed to ancient Greece and named after the 16th letter in the Greek alphabet. The pi value represents the ratio of the diameter of a circle divided by its circumference. This ratio is always the same number regardless of the size of the circle. A circle is a geometric shape called a conic section. The diameter of a circle is the longest distance from one side to the other, with half that distance being the radius. The circumference is the distance around the edge of the circle. The pi value is an irrational number approximately equal to 3.1416. This value is used in geometry to define the area and volume of curvilinear shapes and solids. The area of a circle is pi times the radius squared. The volume of a sphere is pi times four-thirds times the radius cubed. In trigonometry a circle is 360 degrees, where each degree represents an angle. Angles can be converted to radians as a measurement unit which is used in trigonometry by the formula one pi radian equals 180 degrees.

Radian to degree conversion:
Two pi radians is a full circle,
since pi radians = 180 degrees,
so two pi converts to 360 degrees.
One-half pi radian is equal to 90 degrees,
one-third pi radians is 60 degrees
and one-fourth pi radians is 45 degrees.
One radian is equal to approximately 57.296 degree

Degrees to radian conversion:
One degree is equal to approximately 0.0175 radians.

Math Mysteries: The pi ratio of two distances in a circle ends up being an irrational number. These two numbers are generated through simple geometry, yet the outcome is not a rational number. The definition of a rational number is that it can be expressed as a ratio. This special number pi is an irrational ratio and the area of a circle and the volume of a sphere can never be exactly known.