half-angle formula
The trigonometric functions of the half of an angle that are expressed in terms of separate functions of the angle.
sin(x/2)
= ±[(1 - cosx)/2]
^{1/2}
cos(x/2)
= ±[(1 + cosx)/2]
^{1/2}
tan(x/2)
= sinx/(1 + cosx)
= (1 - cosx)/sinx
Related Terms:
addition formula
,
double-angle formula
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