Thread: Rearranging simulataneous equation into y = mx + c

1. Rearranging simulataneous equation into y = mx + c

I haven't done maths in years as I thought I wouldn't ever do it again after school but it has cropped up in university and I've forgotten it all.
So...

I need to plot the following on a graph in Excel
3x + y - 6 = 0 (i)
y - 3x + 2 = 0 (ii)

I need to rearrange this, right?
I was thinking (this is probably wrong)...

(i): y = -3x - 6
(ii): y = 3x + 2

I would appreciate any help and also how to rearrange equations like this. I understand you have to make y the subject here and that you change the sign of something...but I don't know what. :s

Thanks.

2. Originally Posted by Jamie88
I haven't done maths in years as I thought I wouldn't ever do it again after school but it has cropped up in university and I've forgotten it all.
So...

I need to plot the following on a graph in Excel
3x + y - 6 = 0 (i)
y - 3x + 2 = 0 (ii)

I need to rearrange this, right?
I was thinking (this is probably wrong)...

(i): y = -3x - 6
(ii): y = 3x + 2

I would appreciate any help and also how to rearrange equations like this. I understand you have to make y the subject here and that you change the sign of something...but I don't know what. :s

Thanks.
The secret in elementary algebra is what you do to one side of an equation you also do to the other side.

3x + y - 6 = 0

Now subtract 3x from both sides to get:

3x +y - 6 -3x = -3x

or:

y - 6 = -3x

Now add 6 to both sides:

y - 6 + 6 = -3x + 6

or:

y = -3x + 6

RonL

3. Originally Posted by CaptainBlack
The secret in elementary algebra is what you do to one side of an equation you also do to the other side.

3x + y - 6 = 0

Now subtract 3x from both sides to get:

3x +y - 6 -3x = -3x

or:

y - 6 = -3x

Now add 6 to both sides:

y - 6 + 6 = -3x + 6

or:

y = -3x + 6

RonL
Okay so this applies to (ii) as well, yeah?
(ii) y - 3x + 2 = 0

Do I add the -3x here or subtract it as it is a minus...

4. Originally Posted by Jamie88
Okay so this applies to (ii) as well, yeah?
(ii) y - 3x + 2 = 0

Do I add the -3x here or subtract it as it is a minus...
You add 3x as (-3x)+3x=0 and the idea is to remove this term from the left hand side, so:

y - 3x + 2 + 3x = 3x

or:

y +(-3x+3x) +2 = 3x

so:

y +2 = 3x.

(adding 3x is the same thing as subtracting -3x that is 3x=-(-3x))

RonL

5. So...

y = 3x - 2

?

6. Originally Posted by Jamie88
So...

y = 3x - 2

?
Yes.

-Dan