8 - 3x = 128
what is the value of x?
8 - 3x = 128
Subtract 8 from both sides.
-3x = 120
x = 120/-3
x = -40
You can prove this by substituting -40 for x.
-3(-40) + 8 = 128
120 + 8 = 128
Wait, why would you subtract 8 from both sides. I thought that you do the opposite and the opposite of -8 is +8... so confused... :)
You want to get the known numbers on one side of the equation and the unknowns on the other.
To do that you have to get rid of the 8 on the left side. But when you do that, you must add it to the other side.
Look at this very simple problem.
1 + 2x = 5