x 1-x2-x3+x4=0 ( 1)

x 1-x2-x3-3x4=0 (2)

x 1-x2-2x3+3x4=0 (3)

Solution:

( 1)-(2)，4x4=0，x4=0。

x 1-x2-x3 = x 1-x2-2x 3 = 0，x3=0

So X 1-x2 = 0, x 1=x2,

The solution of the equation is: x 1=x2, x3=0, x4=0. x 1∈R，x2∈R .