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"Whenever two men meet there are really six people present. There is each man as he sees himself, each man as the other sees him, and each man as he really is." -William James

$$\cos x = \sum\limits_{n = 0}^\infty {\frac{{\left( { - 1} \right)^n x^{2n} }}{{\left( {2n} \right)!}}}$$