Question 330636
You mean you know the arc length and the angle corresponding to the arc length. 
If {{{AL}}} is arc length, {{{C}}} is circumference, {{{theta}}} is the angle in radians, then
{{{AL/theta=C/(2*pi)}}}
{{{C=(2*pi*AL)/theta}}}
Since the circumference is the arc length when the corresponding angle is {{{2*pi}}} radians. 
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If the angle is in degrees, then,
{{{AL/theta=C/360}}}
{{{C=(360*AL)/theta}}}