straight line on graph

[xylia]

I'm having some difficulty solving this problem,

we have x on the graph and its unknown , the gradient is of a straight line is 2.3 x10^4 the interception on the y axis is 5.8 x10^4 m we know y is 6.2x10^5 m

i need to find x

 

so i tried rearranging the equation

y=mx+c to get x=y/m-c but i get a rely high number so I'm guessing its not correct

please help me

[Lizzie L]

I'm having some difficulty solving this problem,

we have x on the graph and its unknown , the gradient is of a straight line is 2.3 x10^4 the interception on the y axis is 5.8 x10^4 m we know y is 6.2x10^5 m

i need to find x

 

so i tried rearranging the equation

y=mx+c to get x=y/m-c but i get a rely high number so I'm guessing its not correct

please help me

 

 

Well, those are big numbers!

 

Can you write down the equation for the line?

 

Is it y=2.3 x10^4x + 6.2x10^5?

 

If so, you just need to think again about your rearrangement

[Tim the plumber]

25 years since I did any of this but 24.43 is my answer.

[xylia]

right because y=mx

[Lizzie L]

Well, y=mx+c right? That's the equation for your line.

 

You know that y is 6.2x10^5

You know that the intercept, c is 5.8 x10^4

 

And you know that m (presumably) is 2.3 x10^4

 

So, as you say, you just have to rearrange:

 

y = mc + c. Subtract c from both sides:

 

y - c = mx. Now divide both sides by m, and then substitute your known values

Edited April 10, 2014 by Lizzie L

[xylia]

yes right but isn't that what i did?

[Lizzie L]

yes right but isn't that what i did?

 

Well,

 

y=mx+c doesn't turn into x=y/m-c !

 

I'm trying to get you to do the last line yourself! First subtract c from both sides:

 

y- c = mx + c - c.

 

So that gets you to

 

y-c = mx

 

Now divide both sides by m. That gets you to

 

(y-c)/m = mx/m, Right?

 

Which gets you to....get it?

[xylia]

(y-c)/m=x

[Lizzie L]

Yup. Now substitute your values for y, m and c, and you are done

Edited April 10, 2014 by Lizzie L