How to obtian the coefficients $a_i$

\[\frac{1}{{\left( {1 - {q^{x + 1}}} \right)\left( {1 - {q^{x + 2}}} \right) \cdots \left( {1 - {q^{x + m}}} \right)}} = \frac{{{a_1}}}{{1 - {q^{x + 1}}}} + \frac{{{a_2}}}{{1 - {q^{x + 2}}}} + \cdots + \frac{{{a_m}}}{{1 - {q^{x + m}}}}\]