$\"\"$

From the figure radius of the circle is $\"\"$ and length of the arc is $\"\"$ .

Arc length of the circle : $\"\"$ .

Where,

$\"\"$ central angle

$\"\"$ = radius of the circle.

Substitute $\"\"$ and $\"\"$ in $\"\"$ .

$\"\"$

Divide each side by 2.

$\"\"$ radians.

$\"\"$

The central angle is $\"\"$ radians.