customizing trendlines - square root function?

[Erin Cole]

I have some data that theoretically should plot like a square root function.

I need to apply a trendline, but customize it to show me what the data would look like as a square root....

would that be a power function or an exponential? the data look more like a log function, but that doesn't really work for me...as I decrease on the x axis, the data turn more sharply downward on the y-axis than the log trendline...

how do I further customize power, log, or exponential trendlines?

thanks so much....

 

[macajm]

square root is a power function (ie to the power of 0,5)
My test data (y=sqrt(x) ) gave a perfect fit with a power trendline.