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1°)
$\small (+8x^5y^2) : (-16x^3y^2)=$
$\small =\dfrac{8x^5\cancel{y^2}}{-16x^3\cancel{y^2}}=$
$\small = -\dfrac{\cancel8^1x^5}{\cancel{16}_2x^3}=$
$\small = -\dfrac{1}{2}x^{5-3}=$
$\small = -\dfrac{1}{2}x^2 $ o anche $\left(= -\dfrac{x^2}{2}\right)$
2°)
$\small (+9a^3b^4) : (+27a^3b)=$
$\small = \dfrac{\cancel9^1\cancel{a^3}b^4}{\cancel{27}_3\cancel{a^3}b} =$
$\small = \dfrac{1}{3}b^{4-1}=$
$\small = \dfrac{1}{3}b^3$ anche scritto $\left(= \dfrac{b^3}{3}\right)$