86:[2.(2.x-1)2-7]+42 = 2.32
86:[2.(2.x-1)2-7]+16 = 2.9
86:[2.(2.x-1)2-7]+16 = 18
86:[2.(2.x-1)2-7] = 18-16
86:[2.(2.x-1)2-7] = 2
2.(2.x-1)2-7 = 86:2
2.(2.x-1)2-7 = 43
2.(2.x-1)2 = 43+7
2.(2.x-1)2 = 50
(2.x-1)2 = 50:2
(2.x-1)2 = 25
(2.x-1)2 =52
\(\Rightarrow\)2.x-1 = 5
2.x = 5+1
2.x = 6
x = 6:2
x = 3