[tex] \frac{1}{ {2}^{2} } + \frac{1}{ {3}^{2} } = \frac{1}{4} + \frac{1}{9} \\ \\ aducem \: la \: acelasi \: numitor \\ \\ \frac{9}{36} + \frac{4}{36} = \frac{13}{36} [/tex]
