Question: Finding out whether or not a function is positive?

If I have a function of R.  I want to find out if there is an R value for which the function is positive.

And if possible, what that R value is.  I graphed the function for a whole bunch of ranges of R values, but there's only so much I can do with graphing.

This is somewhat similar to command in  MATLAB "isreal(p)" which returns true if p is a real number and false if p is imaginary, but instead I want to know if the function is positive for ANY values of R. 

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