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Daca 3a+2b+4c=494 si b+2c=157,calculati ab+2ac

Răspuns :

3a+2b+4c=494⇒3a+2(b+2c)=494⇒3a+2*157=494⇒3a=494-314⇒a=60
 b+2c=157

ab+2ac=a(b+2ac)=60*157=9420