Plot[x^3/(Exp[x] - 1), {x, 0, 12}, Frame -> True]

\(\(Plot[x^3/\((Exp[x] - 1)\), {x, 2.8, 2.83}, Frame -> True]
\)\)

Plot[1/(x^5*(Exp[1/x] - 1)), {x, 0. , 2}, Frame -> True]

Plot[1/(x^5*(Exp[1/x] - 1)), {x, 0.19, 0.21}, Frame -> True]