5678, 5687,5768,5786,5876,5867,6578,6587,6758,6785,6875,6857,7865,7856,
7658,7685,7568,7586,8765,8756,8657,8675.,8576,8567.
A4-a2=0,4
a1+3d-(a1+d)=0,4
2d=0,4
d=0,4;2=0,2
S6=9
(2a1+5d)*6/2=9
(2a1+5*0,2)*3=9
2a1+1=9:3=3
2a1=3-1=2
a1=2:2
a1=1
5(у-2x)=1/2z
5y-10x=0.5z
5y=0.5z+10x /5
y=0.1z=2x
------------------------------
5(у-2x)=1/2z
5y-10x=0.5z
-10x=0.5z-5y
10x=5y-0.5z /10
x=0.5y-0.05z
-----------------------------------
5(у-2x)=1/2z
5y-10x=0.5z
-0.5z=10x-5y
0.5z=5y-10x /0.5
z=10y-20x