12х+31=23х-2
12х-23х = -2-31
- 11х= -33
х= -33 : (-11)
х= 3
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2(х-2)-1= 5(х-2) -7
2х-4-1=5х-10-7
2х-5=5х-17
2х-5х=-17+5
-3х = -12
х=-12 : (-3)
х= 4
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9х+11=3х-1
9х-3х=-1-11
6х=-12
х= -12 : 6
х= -2