Definition:Formal Derivative of Polynomial

Definition
Let $K$ be a field.

Let $K \left[{X}\right]$ be the ring of polynomial forms over $K$.

Let $f = a_0 + a_1 X + \cdots + a_n X^n \in K \left[{X}\right]$.

The formal derivative $f'$ of $f$ is the polynomial:


 * $f' \left({X}\right) = a_1 + 2 a_2 X + \cdots + n a_n X^{n-1}$