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Решите задачу:

$( \frac{ x^{2} -5x}{ x^{2} -10x+25} + \frac{25}{ x^{2} -25})\cdot \frac{5+x}{125- x^{3} } = \\ =( \frac{x(x-5)}{(x-5) ^{2} }+ \frac{25}{(x-5)(x+5)} )\cdot \frac{5+x}{125- x^{3} } = \\ =( \frac{x}{(x-5)} + \frac{25}{(x-5)(x+5)} )\cdot \frac{5+x}{125-x ^{3} }= \\ = \frac{x(x+5)+25}{(x-5)(x+5)} \cdot \frac{5+x}{(5-x)(25+5x+ x^{2} )}= \frac{ x^{2} +5x+25}{(x-5)(5-x)(25+5x+ x^{2} )} = \\ = \frac{1}{-25- x^{2} } =- \frac{1}{ x^{2} +25}$