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a) $5,78;$
b) $6,\overline5\quad(6,5555\ldots);$
c) $4,3\overline7\quad(4,37777\ldots);$
d) $3,12\overline{43}\quad(3,1243434343\ldots);$ → $(3,\overbrace{12}^{(1)}\overbrace{43434343\ldots}^{(2)}).$
Note:
$^{(1)} = $ antiperiodo;
$^{(2)} = $ parte periodica.