Question 1003581
The arc is some length {{{alpha}}}.
radius, given as 21;  full circumference is  {{{2*pi*21=42pi}}}.


Perimeter of sector is given as 64;
{{{2*21+alpha=64}}}
{{{alpha=64-2*21}}}
{{{alpha=22}}}, centimeter length units.


A full circle central angle measure would be {{{2pi}}}.
The example central angle is a fraction of {{{2pi}}}.


Central Angle Measure in radians,  {{{(22/42pi)*2pi}}},
{{{highlight(22/21)}}} RADIANS


As degrees,  {{{(22/21)*360/(2pi)=(22*360)/(21*2*pi)=(11*360)/(21*pi)=60*degrees}}}