1)
5х+12=8х+30
5x-8x=30-12
-3x=18
x=18:(-3)
x=-6
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5*(-6)+12=8(-6)+30
-30+12=-48+30
-18=-18
2)
6х-19=-х-10
6x+x=-10+19
7x=9
x=9:7
x= 1 2/7
------------------------
6*9/7-19=-9/7-10
54/7 -19=-10 9/7
7 5/7 -19 = -11 2/7
-11 2/7 = -11 2/7
3)
0,1х+9=0,2х-4
0,2-0,1x=9+4
0,1x=13
x=13:0,1
x=130
-----------------------
0,1*130+9 = 0,2*130-4
13+9=26-4
22=22