[tex]a - prima \: zi[/tex]
[tex]b - a \: doua \: zi[/tex]
[tex]c - a \: treia \: zi[/tex]
[tex]a + b + c = 65[/tex]
[tex]b = 2a[/tex]
[tex]a = \frac{b}{2} [/tex]
[tex]b = c - 5[/tex]
[tex]c = b + 5[/tex]
[tex] \frac{b}{2} + b + b + 5 = 65[/tex]
[tex] \frac{b}{2} + 2b = 65 - 5[/tex]
[tex] \frac{b}{2} + 2b = 60 \: | \times 2[/tex]
[tex]b + 4b = 120[/tex]
[tex]5b = 120[/tex]
[tex]b = \frac{120}{5} [/tex]
[tex]b = 24[/tex]
[tex]a = \frac{b}{2} [/tex]
[tex]a = \frac{24}{2} [/tex]
[tex]a = 12[/tex]
[tex]c = b + 5[/tex]
[tex]c = 24 + 5[/tex]
[tex]c = 29[/tex]