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I want to illustrate the calculation of lateral area cone trunk. I can do the first and the third drawing but I can't do the second. enter image description here

\documentclass{article}

\usepackage{tikz}   

\begin{document}            

\begin{center}

\begin{tikzpicture}

\draw (-1,0) arc (180:360:1cm and 0.5cm);

\draw (-1,0) arc (180:0:1cm and 0.5cm);

\draw (-2,-3) arc (180:370:2cm and 1cm);

\draw[dashed] (-2,-3) arc (180:10:2cm and 1cm);

\draw(-2,-2.9)  -- (-1,0);

\draw(2,-2.9)   -- (1,0);

    \draw [dashed](-2,-2.9)  -- (2,-2.9);

    \draw[dashed](0,-2.9) --(0,0);

    \draw[dashed](-0.6,0.4,) --(1,0);

    \node at (0.3,-1.4) {\textbf{h}};

    \node at (0,-3.2) {\textbf{R}};

    \node at (0,0.2) {\textbf{r}};

\shade[left color=blue!5!white,right color=blue!60!white,opacity=0.3] (-1,0) arc (180:360:1cm and 0.5cm) -- (2,-3) arc (360:180:2cm and 1cm) -- cycle;

\shade[left color=blue!5!white,right color=blue!60!white,opacity=0.3] (0,0) circle (1cm and 0.5cm);

\end{tikzpicture}

\end{center}

\end{document}
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2 Answers 2

Reset to default
4

You may add something like the following (using polar coordinates to specify the points) inside your tikzpicture:

\begin{scope}[xshift=5cm,yshift=1cm]
\draw (-120:2cm) arc (-120:-60:2cm);
\draw (-120:4cm) arc (-120:-60:4cm);
\draw(-120:2cm) -- (-120:4cm);
\draw(-60:2cm) -- (-60:4cm);
\node at (-90:1.5cm) {$2\pi r$};
\node at (-90:4.5cm) {$2\pi R$};
\end{scope}
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2

Like this:

enter image description here

With this code (adapted from the OP and the MattAllegro's answer):

\documentclass[margin=5pt]{standalone}

\usepackage{tikz,marvosym}   
\pagecolor{gray!15}
\begin{document}            
        \begin{tikzpicture}[scale=1.5]
            \filldraw[cyan,fill=violet!60,opacity=.5] (0,0) ellipse(1cm and .5 cm);
            \filldraw[cyan,fill=magenta!10,opacity=.5] (0,-3) ellipse(2cm and 1 cm);
            %\draw[cyan] (-2,-3) arc (180:370:2cm and 1cm);
            \draw[cyan,dashed] (-2,-3) arc (180:10:2cm and 1cm);
            \draw[cyan] (-2,-2.9)  -- (-1,0) node[pos=.5,black,sloped,above] () {$\sqrt{h^2+(R-r)^2}$};
            \draw[cyan] (2,-2.9) -- (1,0);  
            \draw[dashed] (-1,0)--(-1,-3) node[pos=.5,fill=white] () {\bfseries $h$};
            \draw [dashed](-2,-2.9)  -- (0,-2.9) node[pos=.5,below] () {\bfseries $R$};
            \draw[dashed](0,-2.9) --(0,0) node[pos=.5,fill=white] () {\bfseries $h$};
            \draw[dashed](-0.6,0.4,) --(0,0) node[pos=.5,fill=white] () {\bfseries $r$};
            \draw (-1.5,-2.9) node[fill=white] () {\bfseries $R-r$};
            \shade[left color=blue!5!white,right color=blue!60!white,opacity=0.3] (-1,0) arc (180:360:1cm and 0.5cm) -- (2,-3) arc (360:180:2cm and 1cm) -- cycle;
            %\shade[left color=blue!5!white,right color=blue!60!white,opacity=0.3] (0,0) circle (1cm and 0.5cm);
            \draw (2.1,-3.1) node[rotate=-60] () {\Huge \Leftscissors} node[right] () {\Huge $\;\rightarrow \;$} ;
            \draw (3.6,1) node () {\large $S_l=\pi(r+R)h$};
            \draw (3.6,.5) node () {\large $S_t=\pi(r+R)h+\pi\left(r^2+R^2 \right) $};
            \draw (3.6,0) node () {\large $V=\frac{1}{3}\pi\left(R^2+rR+R^2 \right)h $};

        \begin{scope}[cyan,xshift=6cm,yshift=2.2cm,scale=1.5]
                \draw (-120:2cm) arc (-120:-60:2cm) node[pos=.5,black,fill=white] () {$2\pi r$};
                \draw (-120:4cm) arc (-120:-60:4cm) node[pos=.5,black,fill=white] () {$2\pi R$};
                \draw(-120:2cm) -- (-120:4cm);
                \shade[left color=blue!5!white,right color=blue!60!white,opacity=0.3] (-120:2cm) arc (-120:-60:2cm) -- (-60:4cm) arc (-60:-120:4cm) -- cycle;
        \end{scope}
        \end{tikzpicture}
\end{document}
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