Error matemático del paquete PGF: operador desconocido `c' o `co' (en '{4cos(deg(x))}')

Question

Para el código que figura a continuación, aparece el siguiente error:

Error matemático del paquete PGF: operador desconocido c' orco' (en '{4cos(deg(x))}').

Error matemático del paquete PGF: operador desconocido p' orpi' (en '2pi').

Error matemático del paquete PGF: operador desconocido p' orpi' (en '2pi').

Por favor ayuda

 \documentclass{article}
    \usepackage{graphicx} % Required for inserting images
    
    \usepackage{amsmath}
    \usepackage[a4paper, total={6in, 8in}]{geometry}
    \usepackage{graphicx} % Required for inserting images
    \usepackage{pgfplots}
    \usepackage{tikz}
    \usetikzlibrary{shapes.geometric, arrows}
    
    \begin{document}
    
    \begin{center}
    \begin{tikzpicture}[scale=0.8]
    \draw[<->] (-4,0) -- (4,0) node[right] {$x$};
    \draw[<->] (0,-4) -- (0,4) node[above] {$y$};
    \draw[dashed] (0,-4) -- (0,4);
    \draw[blue,thick,->] plot [domain=0:2pi,samples=100] ({0},{4cos(deg(x))});
    \draw[red,thick,->] plot [domain=0:2pi,samples=100] ({0},{-4cos(deg(x))});
    \end{tikzpicture}
    \end{center}
    
    
    \end{document}

Answer 1

Prueba esto:

   \documentclass{article}
   \usepackage{graphicx} % Required for inserting images
   
   \usepackage{amsmath}
   \usepackage[a4paper, total={6in, 8in}]{geometry}
   \usepackage{graphicx} % Required for inserting images
   \usepackage{pgfplots}
   \usepackage{tikz}
   \usetikzlibrary{shapes.geometric, arrows}
   
   \begin{document}
   
   \begin{center}
     \begin{tikzpicture}[scale=0.8]
       \draw[<->] (-4,0) -- (4,0) node[right] {$x$};
       \draw[<->] (0,-4) -- (0,4) node[above] {$y$};
       \draw[dashed] (0,-4) -- (0,4);
       \draw[blue,thick,domain=0:{2*pi},samples=100] plot  ({\x},{4*cos(\x r)});
       \draw[red,thick,domain=0:{2*pi},samples=100] plot ({\x},{-4*cos(\x r)});
     \end{tikzpicture}
   \end{center}
   
   
   \end{document}