I have two circles of radii `4` and `5` drawn in blue and line segments drawn in purple between them so that the endpoints of them are perpendicular to radii of them. To give the impression that this depiction represents a conveyor belt, I will add two `arc` commands drawn in purple and will reduce the radii of the circles from `5cm` and `4cm` to `5cm-0.2pt` and `4cm-0.2pt`. Why is the command for drawing the circle `2pt` less than `5cm` not being implemented? This is the command that was misinterpreted.

```
\draw[blue] (center_of_first_circle) circle ({5cm - 0.2pt});

```

In my code, I used the following command to render a diagram that I am looking to modify.

```
\draw[blue] (center_of_first_circle) circle (5);

```

Here is my code.

```
\documentclass[10pt]{amsart}
\usepackage{mathtools,array}

\usepackage{tikz}
\usetikzlibrary{calc,positioning,intersections}

\begin{document}

\begin{tikzpicture}[x=0.25cm, y=0.25cm]

%The centers of a circle of radius 4 and a circle of radius 5 are at a distance of 16 from each other. Two line segments
%are to be drawn between them so that they are tangent to the circles. (It is a sketch of a conveyor belt.) The radii to
%the point of tangency of the same line segment are parallel to each other. The centers of the circles are located on the
%x-axis - the center of the circle of radius 5 is centered at the origin, and the center of the circle of radius 4 is
%centered at (16,0). If \theta is the measure of the angle between the x-axis and the two radii, the slope of
%the line segment is sin\theta/(16 - cos\theta). So, the slope of the radii is (cos\theta - 16)/sin\theta. The slope is
%also tan\theta.
%x = 5cos\theta.
%x^2 + ((cos\theta - 16)/sin\theta)^2*x^2 = 5^2.
%tan\theta=(cos\theta - 16)/sin\theta.
%This is a quartic equation in the variable x. The solution is 5*sqrt(65/2 - 4*sqrt(66)). The point of tangency on the circle
%of radius 5 is
%(5*sqrt(65/2 - 4*sqrt(66)), 5*sqrt(4*sqrt(66) - 63/2)).
%
%
\path (0,0) coordinate (center_of_first_circle) (16,0) coordinate (center_of_second_circle);
%
%
%
\path let \n1={5*sqrt(65/2 - 4*sqrt(66))}, \n2={5*sqrt(4*sqrt(66) - 63/2)} in coordinate (a_point_of_tangency_on_bigger_circle) at (\n1,\n2);
\path let \n1={5*sqrt(65/2 - 4*sqrt(66))}, \n2={5*sqrt(4*sqrt(66) - 63/2)} in coordinate (another_point_of_tangency_on_bigger_circle) at (\n1,-\n2);
%
\path let \n1={2*sqrt(66)}, \n2={sqrt(64*sqrt(66)-504)} in coordinate (a_point_of_tangency_on_smaller_circle) at (\n1,\n2);
\path let \n1={2*sqrt(66)}, \n2={sqrt(64*sqrt(66)-504)} in coordinate (another_point_of_tangency_on_smaller_circle) at (\n1,-\n2);
%
%
\draw (a_point_of_tangency_on_bigger_circle) -- (a_point_of_tangency_on_smaller_circle);
\draw (another_point_of_tangency_on_bigger_circle) -- (another_point_of_tangency_on_smaller_circle);
%
%
%
\draw[blue] (center_of_first_circle) circle (5);
\draw[blue]  (center_of_second_circle) circle (4);

\end{tikzpicture}

\end{document}

```