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deriving trig formula

derive the half angle formula for sine, sin (X/2) = squaroot((1-cosx)/2) from a double angle formula for cosine.

$cos(2u)=1-2sin^{2}(u)$

$2sin^{2}(u)=1-cos(2u)$

$sin^{2}(u)=\frac{1-cos(2u)}{2}$

Now, use the substitution $u=\frac{x}{2}$

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