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Relationship between inner and outer radius of a two concentric circles

otlconcepts

New member
May 15, 2020
1
If i have two circles that say 24" apart from each other. one inside the other.
and i know the radius of the inside circel, how can i calculate the outside radius
 

Joppy

Well-known member
MHB Math Helper
Mar 17, 2016
256
Did you draw a picture?

\begin{tikzpicture}

\draw[thick,red] (0,0) circle (4);
\draw[->,thick,red] (0,0) -- (4, 0) node[below, xshift=-1cm] {$r_2$};
\draw[thick,blue] (0,0) circle (2);
\draw[->, thick, blue] (0,0) -- (2, 0) node[below, xshift=-0.75cm] {$r_1$};

\end{tikzpicture}

$r_2 - r_1 = 24"$ right? And you know $r_1$.
 
Last edited:

MarkFL

Administrator
Staff member
Feb 24, 2012
13,735
Hello, and welcome to MHB! :)

Suppose \(r\) is the radius of the inner circle and \(R\) is the radius of the inner circle, where \(k\) is the difference between the two radii:

\(\displaystyle R-r=k\)

mhb_0015.png