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# Transformation of graphs help watch

1. Hi guys,
So I'm doing a project on modelling the spread of Ebola. My task is to model a graph to fit the number of cases and deaths in various countries, however I have to find the function on paper, as my teacher said it is too easy using the computer.
I have decided the graph is exponential in nature, and will try and use the function in the form ae^bx +c.
If I have the data on a graphing program, how do I find the values of a and b? My teacher said to use the average x value to find the stretch value, but from there on I'm stuck.
So, how do I find the a and b coefficients from a set of data?
Thanks
2. (Original post by samiito)
Hi guys,
So I'm doing a project on modelling the spread of Ebola. My task is to model a graph to fit the number of cases and deaths in various countries, however I have to find the function on paper, as my teacher said it is too easy using the computer.
I have decided the graph is exponential in nature, and will try and use the function in the form ae^bx +c.
If I have the data on a graphing program, how do I find the values of a and b? My teacher said to use the average x value to find the stretch value, but from there on I'm stuck.
So, how do I find the a and b coefficients from a set of data?
Thanks
If you have y=ae^(bx)+c and set x=0 then the value of the y-intercept will be equal to a+c (rearrange for a). Now pick two points on the graph and solve simultaneously for b.
3. (Original post by SherlockHolmes)
If you have y=ae^(bx)+c and set x=0 then the value of the y-intercept will be equal to a+c (rearrange for a). Now pick two points on the graph and solve simultaneously for b.
Thank you for this.
If I wanted to make my model as accurate as possible, would it be best to pick the largest and smallest x values?
4. (Original post by samiito)
Thank you for this.
If I wanted to make my model as accurate as possible, would it be best to pick the largest and smallest x values?
It would probably be best to find multiple values of b and then calculate an average.
5. (Original post by SherlockHolmes)
It would probably be best to find multiple values of b and then calculate an average.
Ok, thank you.
when you said previously to set x=0, do I have to set it to 0? Also, I don't see how I can isolate either a or c as they are both unknowns.
6. (Original post by samiito)
Ok, thank you.
when you said previously to set x=0, do I have to set it to 0? Also, I don't see how I can isolate either a or c as they are both unknowns.
Actually, I don't think it is possible with my method. You have three unknowns a,b,c but can't get 3 equations.

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Updated: January 31, 2015
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