(1)*10,
8x-9y=20,
(2)*3,
18x-9y=7.5,
相减,
10x=12.5,
x=5/4,
y=10/9问题中是9y,不是0.9y.(1), 0.8x-9y=2, (2)*3, 18x-9y=7.5, 相减， 17.2x=5.5, x=55/172, y=-25/129