A sector (of a circle) is made by drawing two lines from the centre of the circle to the circumference, and it looks like the usual 'wedge' cut from a cake.
There are two special cases.
If the angle is 180 degrees then the sector is a semi-circle.
If the angle is 360 degrees then the sector is a full circle.
Clearly the angle cannot be greater than 360 degrees.
Where (for brevity) it says 'radius', 'arc' and so on, it should, more correctly, be something like 'length of radius' or 'arc-length' etc, and 'angle' means 'angle at the centre'.
A problem not dealt with by this calculator is where the length of the chord (c) and the height (h) between the chord and arc are known, and it is required to find the radius (r).r = (c² / 8h) + (h / 2)In words: c squared divided by 8h plus (h divided by 2)
If the perimeter is needed, add together the lengths of
radius + radius + arc