Question

2*a+b=5
2*b+3*c=7
Atunci calculati:4*a+8*b+9*c!!

Answer 1

2a+b=5 | *2 ⇒ 4a+2b=10     |
2b+3c=7 | *3 ⇒ 6b+9c=21   |   + (Adunam cele doua relatii)

4a+2b+6b+9c=10+21
4a+8b+9c=31

Answer 2

$2a+b=5 \ \ \ |(*2) \\\\ \underline{4a+2b=10} \\\\ \\ 2b+3c=7 \ \ \ |(*3) \\\\ \underline{6b+9c=21} \\\\\\ \hbox{Adunam cele 2 relatii si obtinem:} \\\\ 4a+2b+6b+9c=10+21 \\\\ \boxed{\boxed{4a+8b+9c=31}}$