How to have corectly scaled intervals on the same line with some text?

Question

I want the (-infty, -b/2a] interval to be scaled as the big one, but, at the same time, to came in line after the text. The one that's with the text is smaller. How can I remediate this?

Answer 1

On suggestion of the user @koleygr.

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath,amssymb}
\begin{document}
Never use double dollar for an equation!
\begin{enumerate}
     \item $a>0 \implies $ \ldots pe $\displaystyle\left(-\infty, -\frac{b}{2a}\right]$
\end{enumerate}
\end{document}