Asked by Christabelle

8 - 3x = 128
what is the value of x?
Answered by Ms. Sue
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
Answered by Christabelle
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... :)
Answered by Ms. Sue
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



Answered by Christabelle
so the answer to that problem would be x = 2?
Answered by Ms. Sue
Right.

Answered by Christabelle
thank you :) I get it now
Answered by Ms. Sue
You're welcome! And congratulations! :-)
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