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Daca 2•a+b=5 si 2•b+3•c=7, calculati 4•a+8•b+9•c.

Răspuns :

2•a+b=5 /•2 =>4a+2b=10 2b+3c=7 /•3 =>6b+9c=21 8b+4a+9c=31