Through the arc length and radius

The formula for the area of an annulus sector using arc length and radii is:

A = (l / 2) * (r1 + r2)

where A is the area of the sector, l is the length of the arc that defines the sector, r1 is the radius of the inner circle, and r2 is the radius of the outer circle.

An annulus sector is a region of a circular ring that is bounded by two radii and an arc. The two radii are the distances from the center of the ring to the inner and outer edges of the sector, respectively. The arc is the curved portion of the ring that connects the two radii. The area of the annulus sector is the amount of space enclosed by the sector.

To calculate the area of the annulus sector using the given formula, you need to know the length of the arc that defines the sector, as well as the radii of the inner and outer circles. Once you have these values, you can simply plug them into the formula and evaluate to find the area of the sector.

It's worth noting that the formula assumes that the arc length l is measured in radians, and not in degrees. If the arc length is given in degrees, it needs to be converted to radians before it can be used in the formula. This can be done by multiplying the degree measure by π/180, where π is the mathematical constant pi (approximately 3.14159).