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6a+9b=45 ,10b+15c=60afla 2a+5b+3c



Răspuns :

[6a+9b=45  ]:3⇒2a+3b=15
[10b+15c=60 
]:5⇒ 2b+3c=12

2a+3b=15  si  2b+3c=12
se aduna cele doua relatii si ⇒( 2a+3b)+(2b+3c)=15+12⇒2a+5b+3c=27

2a+5b+3c=27