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4a+12b=27-x x=3 afla a+3b

Răspuns :

4a+12b=27-x=>4a+12b=24=>4(a+3b)=24 (impartim totul la 4 (metoda balantei))
=>a+3b=6
4a+12b=27-x
4a+12b=27-3
4a+12b=24
impartim prin 4 ec si obt
a+3b=6