(a^2/b^2 - b^2/a^2)/a^2 + b^2/a^2·b^2
= (a^2·b^{-2} - a^{-2}·b^2)/a^2 + a^{-2}·b^4
= b^{-2} - a^{-4}·b^2 + a^{-2}·b^4
= b^{-2} - a^{-4}·b^2 + a^{-2}·b^4
= (a^4 + a^2·b^6 - b^4) / (a^4·b^2)
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y^5·y^{-2}·y + 3·y^2·y^3·y^{-2}
= y^{5 - 2 + 1} + 3·y^{2 + 3 - 2}
= y^4 + 3·y^3
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1 - x^5/x^7 + 1/x^2
= 1 - x^{5 - 7} + x^{-2}
= 1 - x^{-2} + x^{-2}
= 1