Written by the Fiveable Content Team • Last updated September 2025
Verified for the 2026 exam
Verified for the 2026 exam•Written by the Fiveable Content Team • Last updated September 2025
Definition
Pi (π) is an irrational number approximately equal to 3.14159... It represents the ratio of a circle's circumference to its diameter and appears frequently in mathematical formulas involving circles and trigonometry.
Related terms
Circumference: The circumference of a circle is the distance around its outer edge. It can be calculated using π multiplied by twice its radius (C = 2πr) or using π multiplied by its diameter (C = πd).
Area: The area of a circle is the amount of space enclosed by its boundary. It can be calculated using π multiplied by the square of its radius (A = πr^2).
Trigonometry: Trigonometry is a branch of mathematics that deals with the relationships between angles and sides in triangles. It heavily relies on ratios involving π, such as sine, cosine, and tangent.