Question

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Answer 1

$\frac{1}{ a^{2}+ab } * \frac{ a^{2}- b^{2} }{b} = \frac{1}{a(a+b)} * \frac{(a-b)(a+b)}{b}= \frac{a-b}{ab}$

Answer 2

$\frac{1}{a^{2} +ab} : \frac{b}{a ^{2} -b ^{2} } = \frac{1*(a-b)(a+b)}{a(a+b)*b} = \frac{a-b}{ab}$