D_a \left( {p\left( x \right)} \right) = \frac{{\sum\limits_{i = 0}^{n - 1} {a_i \left[ {\left( {x + a} \right)^i - x^i } \right]} + a_n \sum\limits_{j = 0}^{n - 1} {\left( \begin{array}{c}
 n \\ 
 j \\ 
 \end{array} \right)a^{n - j} x^j } }}{a}