A polynomial asymptote is a function
such that
Since this equation defines a hyperbola, we expect the asymptotes to be lines of the form
.
Ignore the negative root (we don't need it). If
, then we want to find constants
such that
We have
since
forces us to have
. And as
, the
term is "negligible", so really
. We can then treat the limand like
which tells us that we would choose
. You might be tempted to think
, but that won't be right, and that has to do with how we wrote off the "negligible" term. To find the actual value of
, we have to solve for it in the following limit.
We write
Now as
, we see this expression approaching
, so that
So one asymptote of the hyperbola is the line
.
The other asymptote is obtained similarly by examining the limit as
.
Reduce the "negligible" term to get
Now we take
, and again we're careful to not pick
.
This time the limit is
, so
which means the other asymptote is the line
.