Introduction
   Essence
   Memorizing

  Basic Formulas
  Sum and Difference Formulas
  Double & Triple Angle Formulas
  Half Angle Formulas
  Product to Sum Formulas
  Sum to Product Formulas
  All Formulas

   Understanding
   Summarizing
   Examples
   Exercises
   Final thoughts

Basic trigonometric identities

These formulas are very important.  You shouldn't go any farther without knowing them. If you already know them, you can go ahead and continue to the next page.

Quotient Identities
Reciprocal Identities
Pythagorean Identities
Even-Odd Identities
Derived formulas

Quotient Identities

Reciprocal Identities

Pythagorean Identities

Even-Odd Identities

Derived formulas

, if k is an odd integer,

, if k is an even integer.