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Formula for $1/f(x)$ where $f$ is a polynomial
Let $f$ be a polynomial having $n$ distinct real roots:
$$f(x)=(x-x_1)(x-x_2)\dots(x-x_n)$$
Prove that $$\frac{1}{f(x)}=\sum_{k=1}^n \frac{1}{f'(x_k)(x-x_k)}, \: \forall x \in \mathbb{R} - \{x_1,...
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