答案1
\documentclass[tikz,border=3.14mm]{standalone}
\usepackage{amsmath}
\begin{document}
\begin{tikzpicture}
\draw[-latex] (-2,0) -- (5,0) node[below]{$\beta_1$};
\draw[-latex] (0,-2) -- (0,5) node[left]{$\beta_2$};
\fill[opacity=0.2,cyan] (-1,0) -- (0,-1) -- (1,0) -- (0,1) -- cycle;
\coordinate[label=below left:$\widehat{\beta}$] (beta) at (3.5,5);
\fill (beta) circle (1mm);
\foreach \X in {1,1.5,2.5}
{\draw[rotate=45,red] (beta) circle({2*\X} and {0.5*\X});}
\end{tikzpicture}
\end{document}