Question

Найдите А,B (дана система):
{ -2A-B=5
{ A+B=2

Answer 1

прибавим
-A=7
A=-7
B=2-A=2-(-7)=2+7=9

Answer 2

$\left \{ {{-2A-B=5} \atop {A+B=2}} \right. \\-A=7\\A=-7\\\\-7+B=2\\B=2+7\\B=9\\ \\ \left \{ {{A=-7} \atop {B=9}} \right.$