Large space between text and equations when I \begin{equation}

Question

When I do this, there is a large space between the text and the equations. I was wondering if there was a way to solve this. I am using amsmath. Thanks a lot

\textbf{Solution}

\begin{center}
    \begin{equation*}
        (1+x)(1+y)\geqslant{4}
    \end{equation*}
\end{center}

Answer 1

The large space is due to the center environment, which adds vertical unneeded space and does nothing useful, since equation center its contents by default.

So, simply remove the center environment.

MWE

\documentclass{article}
\usepackage{amsmath,amssymb}

\begin{document}
\textbf{Solution}

\begin{equation*}
    (1+x)(1+y)\geqslant{4}
\end{equation*}
\end{document} 

Output

I would also suggest to remove the blank line before the equation environment, so to have the following result:

Answer 2

The equation environment (including equation*) already centres its contents, so there's no need for center. Additionally, center adds vertical space, as discussed in [When should we use \begin{center} instead of \centering?]When should we use \begin{center} instead of \centering?) Only use

\begin{equation*}
  <stuff>
\end{equation*}

If you need to adjust vertical spacing around sparse document elements, then you could consider adjusting certain skips as discussed in How can I decrease spaces between equations? However, that would not be necessary in this case...