Isolating the variable

1. Oct 20, 2004

dumb dumb

k i am in grade 9 have a terrible math teacher and i need help with this stuff here is an example
-5r + 6 =8
so can u please explain to me how to exactly do this stuff.
THX

2. Oct 20, 2004

Pyrrhus

$$-5r + 6 =8$$

Well whatever you do on your equation you must do it on both sides of it.
to get r alone we could substract 6 from both sides so

$$-5r + 6 -6 =8 - 6$$

$$-5r = 2$$

Now could divide by -5 both sides.

$$r = \frac{2}{-5}$$

there you go, was i clear enough?

3. Oct 20, 2004

Chrono

One word of extra advice from someone who almost failed algebra: Make sure you get it the first time, but if not, ask your instructor, or even us, for clarification. But I see that you have done that already. Good luck!

4. Oct 21, 2004

arildno

dumb dumb:
Here's a way you ought to think about an equation:
Think of it as an old-fashioned weight which has two bowls attached to a rod with a fulcrum in the middle, and that that weight must stay in BALANCE all the time.
Such a weight would tip to one side if more weight was added to the bowl on that side than the other.
Hence, the only operations you're allowed to do is:
1.Add/subtract the same amount on both sides
(This would keep the weight in balance)
2.Multiply/divide with the same factor on both sides
This would also keep the weight in balance.
3. Substitute an equal amount to what's in ONE of the bowls:
For example, if you have:
2+3=4x+4, then you can, of course write this as 5=4x+4, since 2+3=5

Last edited: Oct 21, 2004