Partial sums of a generalized class of analytic functions defined by a generalized Srivastava–Attiya operator

Let $f_n(z)=z+\sum_{k=2}^{n} a_k z^k$ be the sequence of partial sums of the analytic function $f(z)=z+ \sum_{k=2}^{\infty} a_k z^k $. In this paper, we determine sharp lower bounds for   $\Re\{f(z)/f_n(z)\}, \Re\{f_n(z)/f(z)\}, \Re\{f'(z)/f'_n(z)\}$ and $\Re\{f'_n(z)/f'(z)\} $. The efficiency of the main result not only provides the unification of the results discussed in the literature but also generates certain new results.