@YuiToCheng If the emphasis is on the asymptotic expansion, that I can see as how the questions are distinct-ish. I do think that the older question should be referenced by the newer question.
@YuiToCheng Also, just for the future, you should try to avoid using display-stye math in titles---it can stretch the vertical space quite a bit, and (I am told) makes the mobile version of the site work poorly. So things like \left and \dfrac should be avoided.
I edited the title to remove the space stretching stuff.