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I would like to get equation for a known graph "speech banana" enter image description here

So, It happens to have be something like two joined $x^2$ equations. One starts on $ (1000,65) $ and other $ (1000,40)$.

So If I would be on linear graph I could just join both $x^2$ something like $ 0.5x^2 $ and $0.45x^2 - 20$ but as I am on semilog graph I do not know what approach to use.

What would be the best approach to get the equation of this kind of graph?

edgarmtze
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You could use the logarithm of $x$ as the input to your quadratic.

So (with base $10$ logarithms) the bottom curve would be something like:

$y = 65+40*(\log_{10}(x)-3)^2 $

Amzoti
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Penguino
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  • @Amzoti - thanks, I need to invest a little time to learn how to produce attractive equations (but, .... old dogs new tricks etc...) – Penguino Aug 13 '13 at 03:55
  • I had the same issue when I started and I guarantee you it is easy. Reminds of the days of WordStar! If you click 'edit', you can see how simple the changes were. Here is what got me started: http://meta.math.stackexchange.com/questions/5020/mathjax-basic-tutorial-and-quick-reference (it is nicely written and easy to follow). Regards – Amzoti Aug 13 '13 at 03:58