\[\left( \frac{a^{2}}{a + 5} - \frac{a^{3}}{a^{2} + 10a + 25} \right)\ :\left( \frac{a}{a + 5} - \frac{a^{2}}{a^{2} - 25} \right) =\]
\[= \frac{5a - a²}{a + 5}\]
\[\left( \frac{{a^{2}}^{\backslash a + 5}}{a + 5} - \frac{a^{3}}{(a + 5)^{2}} \right)\ :\left( \frac{a}{a + 5} - \frac{a^{2}}{(a - 5)(a + 5)} \right) =\]
\[= \frac{5a - a²}{a + 5}\]
\[\frac{a^{2}(a + 5) - a³}{(a + 5)²}\ :\frac{a(a - 5) - a²}{(a - 5)(a + 5)} = \frac{5a - a²}{a + 5}\]
\[\frac{(a^{3} + 5a^{2} - a^{3})(a - 5)(a + 5)}{(a + 5)²(a^{2} - 5a - a^{2})} = \frac{5a - a²}{a + 5}\]
\[\frac{5a²(a - 5)}{- 5a(a + 5)} = \frac{5a - a²}{a + 5}\]
\[\frac{a^{2} - 5a}{- (a + 5)} = \frac{5a - a^{2}}{a + 5}\]
\[\frac{5a - a²}{a + 5} = \frac{5a - a²}{a + 5}.\]