Trigonometric Identities

Trigonometric identities are formulae that exist between the trigonometric functions.

They are useful for solving algebraic problems involving trigonometric functions.

Here is a list of some common trigonometric identities:

Sin^2(A) + Cos^2(A) = 1

      1        = tan^2(A) + 1Cos^2(A)

Sin(2A) = 2Sin(A)Cos(A) 

Cos(2A) = Cos^2(A) - Sin^2(A)

tan(2A) =     2tan(A)                     1 - tan^2(A)

Sin(A+B) = Sin(A)Cos(B) + Cos(A)Sin(B)

Sin(A-B) = Sin(A)Cos(B) - Cos(A)Sin(B)

Cos(A+B) = Cos(A)Cos(B) - Sin(A)Sin(B)

Cos(A-B) = Cos(A)Cos(B) + Sin(A)Sin(B)

tan(A+B) =    tan(A) + tan(B)                         1 - tan(A)tan(B)

tan(A-B) =  tan(A) - tan(B)                     1 + tan(A)tan(B)

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