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daca    a+2xb=5 si b+2xc=91, atunci calculati 5xa+13xb+6xc

Răspuns :

a+2b=5 |·5=>5a+10b=25(1)
b+2c=91|·3=>3b+6c=273(2)
Din (1)+(2)=>5a+13b+6c=(5a+10b)+(3b+6c)=25+273=298