1.
0.5(x-0.2)=0.9x-1.78
0.5x-0.1=0.9x-1.78
0.5x=0.9x-(1.78-0.1)
0.5x=0.9x-1.68
0.9x-0.5x=1.68
0.4x=1.68
x=1.68/0.4
x=4.2
2.
x/3=(2x-11)/5
6x-33=5x
6x-5x=33
x=33
3.
｛x y=9 (1) ｛6x 7y=59 (2)
(1)*7=7x＋7y=63
7x＋7y-6x-7y
=(7x-6x)＋(7y-7y)
=x-0
=x
x=63-59
x=4
y=9-4
y=5第三题有些不懂