[Risolto] Proposizine seconda media

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$\left(\dfrac{21}{8}+x\right) : x = 3,9 : \left(2+\dfrac{2}{5}\right)$

$\left(\dfrac{21}{8}+x\right) : x = \dfrac{39}{10} : \left(\dfrac{10+2}{5}\right)$

$\left(\dfrac{21}{8}+x\right) : x = \dfrac{39}{10} : \left(\dfrac{12}{5}\right)$

applica il metodo dello scomporre come segue: 

$\left(\dfrac{21}{8}+x-x\right) : x = \left(\dfrac{39}{10}-\dfrac{12}{5}\right) : \left(\dfrac{12}{5}\right)$

$\dfrac{21}{8} : x = \left(\dfrac{39-24}{10}\right) : \left(\dfrac{12}{5}\right)$

$\dfrac{21}{8} : x = \dfrac{15}{10} : \left(\dfrac{12}{5}\right)$

$\dfrac{21}{8} : x = \dfrac{\cancel{15}^3}{\cancel{10}_2} : \left(\dfrac{12}{5}\right)$

$\dfrac{21}{8} : x = \dfrac{3}{2} : \left(\dfrac{12}{5}\right)$

$x= \dfrac{21}{8}·\dfrac{12}{5} : \dfrac{3}{2}$

$x= \dfrac{21}{\cancel8_2}·\dfrac{\cancel{12}^3}{5} · \dfrac{2}{3}$

$x= \dfrac{21}{2}·\dfrac{\cancel3^1}{5}·\dfrac{2}{\cancel3_1}$

$x= \dfrac{21}{\cancel2_1}·\dfrac{1}{5}·\dfrac{\cancel2^1}{1}$

$x= \dfrac{21}{1}·\dfrac{1}{5}·\dfrac{1}{1}$

$x= \dfrac{21}{5}$