Question

daca 2a+b=4 si a+b=8,atunci 3a-2b-7=?

Answer 1

$2a+b=4 \\ b=4-2a \\ a+b=8 \Rightarrow a+4-2a=8 \Rightarrow a-2a=8-4 \Rightarrow -a=4 \Rightarrow a=-4 \\ b=4-2a \Rightarrow 4-2 \cdot (-4)=4+8=12 \\ 3a-2b-7=3 \cdot (-4)-2 \cdot 12-7=-12-24-7=-36-7=-43 \\ \boxed{3a-2b-7=-43}$