are periodic with common period so for values of outside the interval they take repeating values (see above).The sign of a sinusoid or cosinusoid can be used to define a normalized square wave.For example, the functions and take values and correspond to square waves with a phase shift of .

Angle sum and difference identities

These are also known as the angle addition and subtraction theorems (or formulae).

The angle difference identities for and can be derived

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