Răspuns :
[tex] \left \{ {{a+b=25} \atop {a-b=5}} \right. \ \textless \ =\ \textgreater \ \left \{ {{b=25-a} \atop {a-25+a=5}} \right. \ \textless \ =\ \textgreater \ \left \{ {{b=25-a} \atop {2a=30}} \right. \ \textless \ =\ \textgreater \ \left \{ {{a=15} \atop {b=25-15}} \right. \ \textless \ =\ \textgreater \ \left \{ {{a=15} \atop {b=10}} \right. [/tex]