\begin{tikzpicture}
[+preamble]
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
[/preamble]
\begin{axis}[
ticks=none,
xmin=0,
xmax=1.5,
ymin=0,
ymax=1.5,
axis equal,
axis lines=middle,
xlabel=$x$,
ylabel=$y$,
disabledatascaling]
\draw[solid] (1,0) arc (0:90:1);
\draw[solid] (0.3,0) arc (0:30:0.3) node[right, pos=0.5] {$\scriptstyle \theta$};
\draw[solid] ({0.25*cos(30)},{0.25*sin(30)}) arc (30:60:0.25) node[right, pos=0.8] {$\scriptstyle d\theta$};
\path [draw=none,fill=white, fill opacity = 0] (0,0) circle (1);
\draw [line width=0.5mm](0,0) --({cos(30)},{sin(30)});
\draw [line width=0.5mm](0,0)--({cos(60)/cos(30)},{sin(60)/cos(30)});
\draw ({cos(60)/cos(30)},0)--({cos(60)/cos(30)},{sin(60)/cos(30)});
\draw ({cos(30)},{sin(30)})--({cos(60)/cos(30)},{sin(30)});
\draw [line width=0.5mm]({cos(30)},{sin(30)})--({cos(60)/cos(30)},{sin(60)/cos(30)});
\draw ({cos(60)/cos(30)},{sin(60)/cos(30)-0.2}) arc (270:300:0.2) node[right, yshift=0.5, pos=0.1] {$\scriptstyle \theta$};
\end{axis}
\end{tikzpicture}
