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Trigonometric Identities

Eight Fundamental Trigonometric Identities

Key Terms

Negative Angle Identities

The following equations are eight of the most basic and important trigonometric identities. These equations are true for any angle. From them, countless additional identities can be formed. These eight should be memorized.

csc(θ) =    

sec(θ) =    

cot(θ) =    

tan(θ) =    

cot(θ) =    

(sin(θ))2 + (cos(θ))2 = 1    

1 + (tan(θ))2 = (sec(θ))2    

1 + (cot(θ))2 = (csc(θ))2