# How can I draw a dash arc of this circle? [closed]

I want to draw dashed arc AB (from the back) from A to B of circle in this picture. In Oxy plane, coodinates of A is (0,4) and coodinates of A is (3,{-sqrt(7)}) and lie on the circle has the equation x^2 + y^2 =16.

Base on cfr'code, I tried.

\documentclass[12pt,border=3mm]{standalone}
\usepackage{fouriernc}
\usepackage{tikz}
\usepackage{tkz-euclide}
\usetkzobj{all}
\usepackage{tikz-3dplot}
\usetikzlibrary{calc,backgrounds}
\begin{document}
\tdplotsetmaincoords{60}{110}
\begin{tikzpicture}
[scale=1,tdplot_main_coords]

\path
coordinate (O) at (0,0,0)
coordinate (T) at  (0,0,3)
coordinate (B) at  (3,{-sqrt(7)},0)
coordinate (A) at  (0,4,0);
\draw[thick, dashed]
(O)--(T)
(O)--(A)
(A)--(T);

\foreach \v/\position in {T/above,O/below,A/below,B/below} {
\draw[draw =black, fill=black] (\v) circle (1.2pt) node [\position=0.2mm] {$\v$};
}
\begin{scope}[tdplot_screen_coords, on background layer]
\pgfmathsetmacro{\R}{5}%
\pgfmathsetmacro{\r}{4}%
\fill[ball color=cyan!50, opacity=1.0] (T) circle (\R);
\draw[thick] (-\r,0) arc (180:360:\r{} and 2);
\draw [dashed] (\r,0) arc (0:180:\r{} and 2);
\end{scope}
\tkzMarkRightAngle[size = 0.3](T,O,A);
\end{tikzpicture}
\end{document}

With calculating, I solved my problem.

\usepackage{fouriernc}
\usepackage{tikz}
\usepackage{tkz-euclide}
\usetkzobj{all}
\usepackage{tikz-3dplot}
\usetikzlibrary{calc,backgrounds}
\begin{document}
\tdplotsetmaincoords{60}{110}
\begin{tikzpicture}
[scale=1,tdplot_main_coords]
\path
coordinate (O) at (0,0,0)
coordinate (T) at  (0,0,3)
coordinate (B) at  (3,{-sqrt(7)},0)
coordinate (A) at  (0,4,0);
\draw[thick, dashed] (O) -- (A) node[midway,sloped,below] {$r$};
\draw[thick, dashed] (T) -- (A) node[midway,right] {$R$};
\draw[thick, dashed] (T) -- (O) node[midway,left] {$d$};
\foreach \v/\position in {T/above,O/below,A/below,B/below} {
\draw[draw =black, fill=black] (\v) circle (1.2pt) node [\position=0.2mm] {$\v$};
}
\begin{scope}[tdplot_screen_coords, on background layer]
\pgfmathsetmacro{\R}{5}%
\pgfmathsetmacro{\r}{4}%
\fill[ball color=cyan!50, opacity=1.0] (T) circle (\R);
\end{scope}
\tkzMarkRightAngle[size = 0.3](T,O,A);
\draw [thick] (B) arc (318.5:450:4);
\draw [thick, dashed] (A) arc (90:318.5:4);
\end{tikzpicture}
\end{document}

## closed as off-topic by hpekristiansen, Andrew, Stefan Pinnow, Maarten Dhondt, ZarkoSep 22 '17 at 11:39

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question does not fall within the scope of TeX, LaTeX or related typesetting systems as defined in the help center." – hpekristiansen, Andrew, Stefan Pinnow, Maarten Dhondt, Zarko
If this question can be reworded to fit the rules in the help center, please edit the question.

• this is problem of geometry, not latex. starting point of arc i B (if i understood you correctly) but you should determine radius of ellipse which go through B and A. knowing this, drawing in latex is simple than. – Zarko Sep 22 '17 at 8:18
• As @Zarko writes this is purely a geometry problem. You can draw the arc you just need to figure out the angles. – hpekristiansen Sep 22 '17 at 9:34