Thread: 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.

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.

In (i) you start with:

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

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.

In (i) you start with:

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...

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

So...

y = 3x - 2

?

Originally Posted by Jamie88

So...

y = 3x - 2

?

Yes.

-Dan