Dave Horner's Website - Yet another perspective on things...
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To acquire knowledge, one must study; but to acquire wisdom, one must observe.
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Marilyn vos Savant
$$\cos x = \sum\limits_{n = 0}^\infty {\frac{{\left( { - 1} \right)^n x^{2n} }}{{\left( {2n} \right)!}}}$$