Question

Calculați:3/13+1/39;1/25+1/35;2/21+3/28;5/24+7/54

Answer 1

3/13+1/39=|9+1/39=10/39 1/25+1/35=|7+5/175=12/175 2/21+3/28=|8+9/84=17/84 5/24+7/54=|45+28/216=73/216

Answer 2

Inainte de toate, trebuie calculat numitorul comun.
In primul caz este 39. 
In al doilea caz este : 
25=5²
35=5·7
______
c.m.m.m.c.=5²·7=175
In al treilea caz este :
21=3·7
28=2²·7
_______
c.m.m.m.c.=2²·3·7=84
In al patrulea caz este : 
24=2³·3
54=2·3³
_______
c.m.m.m.c.=2³·3³=216

$\frac{3}{13} + \frac{1}{39} = \frac{9}{39} + \frac{1}{39} = \frac{10}{39}$
$\frac{1}{25} + \frac{1}{35} = \frac{7}{175} + \frac{5}{175} = \frac{12}{175}$
$\frac{2}{21} + \frac{3}{28} = \frac{8}{84} + \frac{9}{84} = \frac{17}{84}$
$\frac{5}{24} + \frac{7}{54} = \frac{45}{216} + \frac{28}{216} = \frac{73}{216}$