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Determinati numerele prime intre ele a si b stiind ca 3a+4b=39.

Răspuns :

[tex]3a+4b=39\Rightarrow a= \frac{39-4b}{3} .~Cum~3|39\Rightarrow~3|4b\Rightarrow~3|b\Rightarrow~b\in\{3,6,9\}\\
Nu~convine~b>3~ca~rezulta~3a+48(pt.~b=4)>39\\
Pentru~b=3\Rightarrow a=9.~Nu~convine. \\ Pentru~\boxed{b=6}\Rightarrow \boxed{a=5.}~\underline{Solutie.} \\ Pentru~\boxed{b=9}\Rightarrow \boxed{a=1.}~\underline{Solutie.}[/tex]