(а^-1 - b^-1)/a^-2-2a^-1-b^-1+b^-2 при а=4 b=3

[latex] \frac{ a^{-1}-b^{-1} }{a^{-2}-2a^{-1}*b^{-1}+b^{-2}}= \frac{a^{-1}-b^{-1}}{ (a^{-1}-b^{-1})^{2} } = \frac{1}{a^{-1}-b^{-1}} = \frac{1}{ \frac{1}{a} - \frac{1}{b} } = \\ = \frac{1}{ \frac{b}{ab}- \frac{a}{ab} }= \frac{1}{ \frac{b-a}{ab} }= \frac{ab}{b-a}= \frac{4*3}{3-4}= \frac{12}{-1}=-12 [/latex]