Intersection point in graphs

[Guest]

All,
I have 2 sets of data. One set is directly proportional to the data on
x-axis and the other is is inversely proportional. I want to find out at
which point on the x-axis do the 2 data sets intersect. I can see it
graphically but I need some kind of a formula to spit out that intersection
point.
Any help, suggestions will be appreciated.
Thanks,
R.K.

 

[MrShorty]

General answer:

If we have two functions y1=f(x) and y2=g(x), we find the point(s) of
intersection by setting y1=y2 [f(x)=g(x)]and solving for x.

Specific case:

directly proportional function y1=f(x)=ax
indirectly proportional funciton y2=g(x)=b/x
set them equal ax=b/x -> x^2=b/a -> x=+/- sqrt(b/a)

I leave it to you to decide if you want the positive root or the
negative root, or if I have correctly/incorrectly interpreted the form
of your functions.

 

[Guest]

Thanks Mr. Shorty. Problem I am facing is that thought the relationships are
directly and inversely proportional but they are not perfect linear
equations. In that case how do I solve for intersection point. Is there a
code or formulae?
Thanks again for your help.
RK

 

[MrShorty]

In many cases, it is difficult or impossible to find an algebrai
solution like I suggested above. Back to the general case:

Set spreadsheet up so you have a cell calculating f(x)-g(x) at some
that is reasonable. Then you can use Goal Seek or Solver (Goal Seek i
easier to use, but Solver is more robust) to numerically find the valu
of x that yields f(x)-g(x)=0. There are hazards associated with such
numerical solution (may converge to the wrong solution or may no
converge at all), but this approach is general enough to work in man
cases

 

[Pan]

I believe rk0909 does not has f(x) or g(x)
only has two series of X-Y values
It's possible to build up two equaltion,that just exactly as Excel'
bezier curve for both series
and solve them
however it's too complex,and not worth to do it if you want to do thi
intersection-find job only few time