hello :  X - y - z = -1   ...(1) -x + y + z = 1   ...(2) x + y - z = 1   ...(3) (2) +(3) : 2y = 2       y = 1 subsct in (1) and (2) :    x - z =0                                       -x +z = 0 so x = z  the solution has form : (x , 1 , x )     .... x  in R