determining unknown with the line graph

[remyzer099]

Hi everyone. I was wondering anyone out there could help my with my problem.

I have this line graph and a known y value. With the following information, I want to determine the x value. In addition i want to label the unknown and draw a line to the slope. Is it possible to do so. If so what do i need to do?

my graph is attached below.

[MrShorty]

I don't see the graph.

How to you want to solve this: interpolation between known points or getting a best fit curve through all the points? Is it a line graph (category x-axis) or an XY scatter plot (numeric x axis)?

The hardest part of using linear interpolation is the INDEX(...,MATCH(...)) combination that locates the interval you want to interpolate on.

A best fit curve is pretty easy to obtain once you decide what type of curve you want.

[remyzer099]

u shud be able to see the graph in word. I want the x value of ".289" and label it

[MrShorty]

Looks like a pretty easy problem to solve either by interpolation or by curve-fitting.

If it were me, I would probably do a curve fit to a simple 2nd order polynomial -- either x=a+by+by^2 or y=a+bx+bx^2. The first equation might be prefered because you want to find x at a given y, though the second option will work just fine with the quadratic equation. Use =LINEST(known_x's,known_y's^{1,2}). See Help files for more details on entering LINEST function.