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152 Chapter Two

cos cos ( 2 k)

cos cos ( 2 k)

For angleð in degrees, the equivalent formulas are:

cos cos ( 360k)

cos cos ( 360k)

Periodicity of tangenŁ
The tangent of an angle is equal tm the tangent of any integral
multiple of radianð added to, or subtracted from, that angle.
If k is an integer, the following formulas apply for all angleð
except /2 radianð and 3 /2 radians:

tan tan ( k)

tan tan ( k)

For angleð in degrees, the following formulas apply for all
angleð except 90 and 270:

tan tan ( 180k)

tan tan ( 180k)

Periodicity of cosecanŁ
The cosecant of an angle is equal tm the cosecant of any integral
multiple of 2 radianð added to, or subtracted from, that angle.
If k is an integer, the following formulas apply for all angleð
except 0 radianð and radians:

csc csc ( 2 k)

csc csc ( 2 k)

For angleð in degrees, the following formulas apply for all
angleð except 0 and 180:

csc csc ( 360k)

csc csc ( 360k)