# find a point on a graph

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Hello,

How can I find a point on this curve with y=1000, so what is the x-value when y=1000?

Thanks in advance

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### Answers (2)

John D'Errico
on 10 Mar 2021

You COULD approximate the curve with some function. Best to choose one that can be intelligently extrapolate. Then since you need ot find a value of x where y == 1000, you would either invert the function, perhaps using an analytical inverse if one exists, or using fzero.

Or, since this is fairly well behaved looking curve, you could approximate the data in that plot using a model of the form x(y). Now all you need do is evaluate the functino at y==1000.

We don't have your data, nor any clue as to what a reasonable model might be for all of this. So go and do one of the above.

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Star Strider
on 10 Mar 2021

Try somethiing like this with your data:

x = 10:50; % Create Data

y = 4000 - 80*x; % Create Data

x1k = interp1(y, x, 1000); % Interpolate

figure

plot(x, y, x1k, 1000, 'rs') % Plot Result

xline(x1k, '--k')

yline(1000,'--k')

##### 2 Comments

Star Strider
on 10 Mar 2021

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