在第一象限中画两条线之间的角度

在第一象限中画两条线之间的角度

如何绘制角 theta 并在第一象限中从原点开始的两条线之间放置一个角 theta。

下面是我的代码

\begin{center}
    \begin{tikzpicture}[domain=0:4] 
    \draw[very thin,color=gray] (-0.1,-0.9) grid (3.9,3.9);
    \draw[->] (-0.2,0) -- (4.2,0) node[right] {$x$}; 
    \draw[->] (0,-1.2) -- (0,4.2) node[above] {$y$};
    \draw[color=red]    plot (\x,\x/2)  node[below=2pt] {$\underline{x}$}; 
    \draw[color=blue]   plot (\x,\x)   node[above=2pt] {$Q\underline{x}$};
    \draw[ultra thick,black] ([shift=(30:0.5cm)]2,1) arc (30:60:1.6cm);
 \end{tikzpicture}
\end{center}

答案1

使用anglesTikZ 库并用简单路径绘制线条\draw (<coordinate 1>) -- (<coordinate 2>)::

\documentclass[margin=3mm, tikz]{standalone}
\usetikzlibrary{angles,
                quotes}

\begin{document}
    \begin{tikzpicture}
\draw[very thin,color=gray] (-0.1,-0.9) grid (3.9,3.9);
    \draw[->] (-0.2,0) -- (4.2,0) node[right] {$x$};
    \draw[->] (0,-1.2) -- (0,4.2) node[above] {$y$};
%
\coordinate (O);
\draw[red]   (O) -- (4,2)  coordinate[label=below:$\underline{x}$]  (x);
\draw[blue]  (O) -- (4,4)  coordinate[label=above:$Q\underline{x}$] (q);
%
\pic [draw, thick, <->, 
      angle radius=16mm,angle eccentricity=1.1,"$\theta$"]     {angle = x--O--q};
 \end{tikzpicture}
\end{document}

在此处输入图片描述

或者画一条线作为函数:

\documentclass[margin=3mm, tikz]{standalone}
\usetikzlibrary{angles,
                quotes}

\begin{document}
    \begin{tikzpicture}[domain=0:4] 
\draw[very thin,color=gray] (-0.1,-0.9) grid (3.9,3.9);
    \draw[->] (-0.2,0) -- (4.2,0) node[right] {$x$};
    \draw[->] (0,-1.2) -- (0,4.2) node[above] {$y$};
%
\coordinate (O);
\draw[red]   plot (\x,\x/2)  coordinate[label=below:$\underline{x}$]  (x);
\draw[blue]  plot (\x,\x)    coordinate[label=above:$Q\underline{x}$] (q);
%
\pic [draw, thick, <->, 
      angle radius=16mm,angle eccentricity=1.1,"$\theta$"]     {angle = x--O--q};
 \end{tikzpicture}
\end{document}

结果和以前一样。

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