Hello there. To solve this question, we'll have to remember some properties about circular sectors.
Given a circular sector of a circle with radius R:
Suppose the length of the arc AB is alpha (in radians).
From a well-known theorem about angles in a circle, we know that the angle generating this arc from the center has the same measure, that is:
So we want to determine the area of the sector knowing the radius and the length of the arc.
First, we know that the area of the full circle is given by:
The sector is a fraction of this circle, that means that:
A is a multiple of Asector.
In fact, this proportionality constant is the ratio between the central angle and the angle alpha forming the sector, that is
It is also possible to have alpha in degrees, but we have to convert the center angle to degrees as well, so we get
As we want to solve for the area of the sector, we have that:
Okay. With this, we can solve the question.
We have the following circle:
In this case, notice R = 18 yd and the length of the arc is 80º. This gives us the angle alpha:
Now, we take the ratio between the angle and the total angle applying the formula:
Square the number
Simplify the fraction by a factor of 40º
Multiply the numbers and simplify the fraction
This is the area of this sector.