5x-4y=2 /.2
10x-7y=5 /.(-1)
---------------------------
10x-8y=4
-10x+7y=-5 /+
-----------------------------
-y=-1, y=1
----------------------------
5x-4y=2 /.7
10x-7y=5 /.(-4)
--------------------------------
35x-28y=14
-40x+28y=-20 /+
--------------------------------
-5x=-6, x=6/5, x=1,2
------------------------------
/x,y/=/1,2 , 1/
==================