Ok here I am working on this problem for like 3 hours to no avail.

x1 + x2 = 1

-x1 + x2 + x3 = -1

-1x2 + x3 = 3

I am trying to solve this in matrix form and get the point of multiplaying a cooefficiant but applying it to this set is baffling my mind. Any insights?

is the matrix

1 1 0

-1 1 0

0 -1 1