[Tex/LaTex] Simple partial derivative problem

Question

I have a simple problem with partial derivative symbol, it doesn't work if I try any of these commands:
\partial
\pdiff
\pder

I use sharelatex, and in other projects I could use the \partial symbol.
I have no idea what's the problem, could someone help me?
Thank you!

The code (edited in from a comment):

\documentclass[a4paper,11pt]{article}
\linespread{1}
\usepackage{geometry}
\usepackage{multirow}
\usepackage{anysize}
\usepackage[utf8]{inputenc}
\usepackage[magyar]{babel}
\usepackage[T1]{fontenc}
\usepackage{graphicx}
\usepackage{amsmath}
\usepackage[LGRgreek]{mathastext}
\usepackage{amssymb}
\usepackage{array}
\usepackage{subcaption}
\begin{document}
\begin{equation}
\partial{a}
\end{equation}
\end{document}

The error message: undefined control sequence

Answer 1

The problem arises because you're loading the mathastext package with the option LGRgreek. If you omit this option, the code compiles. If you really need the option LGRgreek, the manual suggests issuing the instruction MTstandardgreek ahead of equations that feature symbols such as \partial.

\documentclass[a4paper,11pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[magyar]{babel}
\usepackage[LGRgreek]{mathastext}

\begin{document}
\begingroup % keep the effect of next instruction local
\MTstandardgreek
\begin{equation}
\partial{a}
\end{equation}
\endgroup
\end{document}