anyone good with excel '07?

[5.0Torx]

hey all

im working on a little excel spreadsheet. ive got a few trendlines approximating some plotted curves, and i'd like to have excel tell me what the x and y coordinates are for the intersection between the two trendlines. Ive been searching around excels help, and google, and have come up with nothing very useful...Can anyone help me out?

 

[mavmavv]

Can you post the spreadsheet or the formulas you are using? That would make it a lot easier for people to help.

 

[NIKwoaC]

I'm sure there is some way to do it in Excel, but I can't say I know off hand. Here is how it is done mathematically:

Take your two equations for each line/curve. Let's say you have

y=3x+7 and y=-2x+4

Because you want the point at which each line intersects, you are looking for the same value in x & y for both equations. So we can say this:

3x+7=-2x+4

So you can solve for the same x value. Once you solve for x (here, x=-0.6), you can solve for y in either of the original equations, and then you have your x & y at which the two lines intersect. In this example, you end with x=-0.6 and y=5.2. You can follow the same method for more complex equations, too, like parabolas, but in that case, you can have more than one intersection point.

 

[5.0Torx]

yeah i know how to do it on paper but i just wanted to do it in excel and have it nice and pretty in my graph

the equations im trying to intersect are

y= -3.6829x^2 + 179.36x + 614.26
and
y= -.7772x^2 + 63.292x + 364.89

i know by inspection that they should meet at around 38-42 for the x value. y should be 1800 ish. (i havent done the calculation by hand yet)