1 answer
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What you see is a function of the programming of particular calculators.
See this:
http://www.coolmath.com/graphit/
type in the function in the function window.
set graph xmin 2.5 x max 3.5 ymin 2 ymax10
hit eval.
Then vary xmin and xmax
I am not certain of the point in this, because what you see is not a function of math, but what a particular calculator does with denominators and how it computes functions with possible zeroes.