\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{gather*}
f(x) = x^2 + 3x +1 \\
g(x) = x^3+4x^2 +3x + 4 \\
h(x) = 4x^4+7x^3+7x^2+3x +1
\end{gather*} 


\begin{gather}
f(x) = x^2 + 3x +1  \\
g(x) = x^3+4x^2 +3x + 4 \\
h(x) = 4x^4+7x^3+7x^2+3x +1 
\end{gather} 


\begin{gather}
f(x) = x^2 + 3x +1 \nonumber \\
g(x) = x^3+4x^2 +3x + 4 \\
h(x) = 4x^4+7x^3+7x^2+3x +1 \nonumber 
\end{gather} 
\end{document}