a) 115 + 5 ( x – 4 ) = 120
5 ( x – 4 ) = 120 – 115
5 ( x – 4 ) = 5
x – 4 = 5 : 5
x – 4 = 1
x = 1 + 4
x = 5
b) 5| x | – 100 = 37 : 35
5| x | – 1 = 32
5| x | = 9 + 1
5| x | = 10
| x | = 2
x = 2 hoặc x = -2
c) 22016 . 2x-1 = 22015
2x-1 = 22015 : 22016
2x-1 = 22015 - 2016
2x-1 = 2-1
⇒ x – 1 = -1
x = -1 + 1
x = 0