C = 2* pi * r ;
is the formula for the circumference of the circle;
in which:
C = the circumference of the circle;
pi , or " π " ; is the symbol for "pi" ;
r = the radius of the circle ;
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To solve for "r" (the radius), divide each side by "2*pi" ;
to isolate "r" (the radius) on one side of the equation;
and to solve for "r" (the radius):
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C = 2*pi*r ;
C / (2*pi) = {2*pi*r} / (2*pi) ;
to get:
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C / (2*pi) = r ;
↔ r = C / (2*pi) .
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