Exercício sobre álgebra elementar

(ENG ARARAQUARA) Simplificar $\phantom{X}\dfrac{\;a^{{}^{\Large -4}}\,-\,b^{{}^{\Large -4}}\;}{\;a^{{}^{\Large -2}}\,-\,b^{{}^{\Large -2}}\;}\phantom{X}$, com $\;{\small 0\neq a^2\neq b^2 \neq 0}$

resposta: $\,\dfrac{a^2+b^2}{a^2b^2}\,$
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