Assuming the triangle is equilateral we can find the radius by finding the length of .
We can create two triangles within and , which forms .
We know is equal to . Thus, we can let and solve for . Doing so, we get .
Now, we use Pythagoreans theorem to find the radius (length ),
So, the area of
Since we know and are both triangles, we know gives us .
Therefore, the area of the sector .
Finally, we just subtract the area of the sector from the area of to get
Sorry, I shoulda drawn a picture...may be confusing.