According to the first three groups of solutions
( 1)+(2): 5x 1-2x3=3 (4)
(2)+(3) De: 7x 1-4x3=3 (5)
(4)*2-(5): 3x 1=3,x 1= 1。
Substitute x 1= 1 into (4) to get the result: x3= 1.
Substituting x 1= 1 and x3= 1 (1) gives the result: x2=2.
Empirical calculation, fortunately, the fourth group also has this solution.