# Coefficient of $$x^2$$

Let $$\color{orange}{C}$$ be the coefficient of $$\color{green}{x^2}$$ in $$\color{purple}{(1-x)(1+2x)(1-3x)(1+4x)\cdots (1+14x)(1-15x)}$$. Find $$\color{orange}{|C|}$$.

[2004 AIME 1 Problem 7]

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