Current Articles | Archives Trigonometric IdentitiesStaff posted on October 23, 2006 | Trigonometric Identities Function Sin Cos Tan Cot Even-Odd Identities Reciprocal Identities Quotient Identities Pythagorean Identities The Pythagorean theorem is a statement about triangles containing a right angle. The Pythagorean theorem states that: "The area of the square built upon the hypotenuse of a right triangle is equal to the sum of the areas of the squares upon the remaining sides." Co-function Identities Sum-Difference Formulas Double Angle Identities Power-Reducing/Half angle formulas Sum-to-Product Formulas Product-to-Sum Derivatives of Trigonometric Functions Laws of Sines and Cosines The law of Sines : The law of Cosines : Please enable JavaScript to view the comments powered by Disqus.