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a+b=7,b+c=11,calculati.a-c

Răspuns :

daca scazi cele doua ecuatii vei obtine a-c=-4
a+b=7 => a=7-b
b+c=11 => c=11-b
a-c <=> 7-b-11-b=7-11 (se reduce b) =-4 => a-c=-4