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Contents
Half Angle Formulae
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Half Angle Formulae
There
are two sets of half angle formulae, one more commonly used than the other.
  These
formulae can easily be found by rearranging the double angle formula for the
cosine function. Whether the function is positive or negative depends on the
quadrant the half angle lies in.
The
other set of half angle formulae are:
Given    Derivation:
From
the double angle formula,
 Drawing
a right angled triangle,
 The
sine and cosine functions are derived from here.
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