Pre-calculus Function Question

I'm not certain whether D is a constant and, if so, whether it is
positive or negative. Maybe it means derivative?

If I assume that D is a positive constant and f is defined for all x
other than 0, then

1. for small positive x, like x=0.001, f is large.
2. for large positive x, like x=1000, f is a little larger than 3D.
3. for small negative x, like x=-1000, f is a little smaller than 3D.
4. for large negative x, like x=-0.001, f is a little larger than 0.

So, as x comes in from negative infinity, the graph decreases from 3D
and approaches 0 as x approaches 0 from the left. Since f does not
take the value 0, it has no local minimum for x<0. As x continues
past 0 and becomes large, the graph just decreases from infinity
towards 3D, but never take on this value. So, again, f has no local
minimum (of 3D).

So, f has no local minimum, unless D=0, in which case, f has a local
minimum for all x not equal to 0.