Logarithmic scaled chart, parabola-shaped curve

[penwright]

I cannot figure out/calculate a parabola-shaped curve (or trendline) that is logarithmically scaled.
I have tried the exponential and quadratic trendlines, but when they are scaled logarithmically they appear in a linear manner.
The chart that I want to create looks like the red arc shapes. - Is there a way to get the graphical formula for an arc shape?
The data is set up as follows:
- Column A: Date (daily)
- Column B: Price (daily)

 

[Anthony47]

Ask Excel to do the job for you:
-rightclick, in the graph, on the data serie
-chose Add Trendline
-in the trendline options window that will open, chose the option that best represent the curve (Exponential, Linear, ... ,Polynomial + grade,...)
-check the options Show Rsquare and Show the equation
The option that represents at best the trend of your data will have the highest Rsquare

At the end of the process you will have the trendline and its equation on the graph for you

The fact that the graph is represented on a logaritmic scale doesn't change the trendline equation

Bye