[2 1 | 1 0 ] • x = [5 | 10]
We multiply by the inverse of
[2 1 | 1 0 ]
det( [2 1 | 1 0] ) = -1
=> [2 1 | 1 0 ]^(-1) = (-1)•[0 -1 | -1 2 ] =
= [0 1 | 1 -2]
=> [2 1 | 1 0 ] • x = [5 | 10]
=> x = [2 1 | 1 0 ]^(-1) • [5 | 10]
=> x = [0 1 | 1 -2] • [5 | 10]
=> x = [0+10 | 5-20]
=> x = [10 | -15]