Question 857145
First we need the distance from (1,1) to (3,5)


*[invoke distance_formula 1,1,3,5]


So the distance from (1,1) to (3,5) is exactly {{{2*sqrt(5)}}} units


This makes the radius to be {{{r = 2*sqrt(5)}}}



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Now use this radius to find the circumference



{{{C = 2*pi*r}}}



{{{C = 2*pi*2*sqrt(5)}}}



{{{C = 2*2*pi*sqrt(5)}}}



{{{C = 4*pi*sqrt(5)}}} This is the exact circumference in terms of {{{pi}}}



{{{C = 28.0992589242}}} Use a <a href="https://www.google.com/search?q=4*pi*sqrt%285%29">calculator</a> to get the approximate circumference