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Daca a+b=17 si b+c=21 calculati 2∙A+7∙B+5∙C

Răspuns :

Răspuns:

a+b=17 I·2

b+c=21 I·5

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2a+2b=34

5b+5c=105

2a+2b+5b+5c=34+105

2a+7b+5c=139