Trigonometric Identities
This is a list of the basic trigonometric identities. You may want to work through a tutorial, with examples and detailed solutions, on Using Trigonometric Identities.
Review of Trigonometric Identities
Pythagoren Identities

sin^{2}x + cos^{2}x = 1

tan^{2}x + 1 = sec^{2}x
 1 + cot^{2}x = csc^{2}x
Reciprocal Identities
 csc x = 1 / sin x
 sec x = 1 / cos x
 cot x = 1 / tan x
The Tangent and Cotangent Identities
 tan x = sin x / cos x
 cot x = cos x / sin x
Identities for Negatives
 sin (x) =  sin x (the sine function is an odd function)
 cos (x) = cos x (the cosine function is an even function)
 tan (x) =  tan x (the tangent function is an odd function)
More References and Links
Trigonometric Identities and Their ApplicationsTrigonometric Formulas and Their Applications