The area is 0.5*pi*r2 where r is the radius.
The angle is totally irrelevant since it will always by 180 degrees for a semicircle!
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The area of the shaded region can be gotten by multiplying the area of the circle by the subtended angle of the sector.
It looks like 3/4 of the area of a circle and it is called a reflex angle
Area of a sector of a circle.
Multiply ( pi R2 ) by [ (angle included in the sector) / 360 ].
A central angle can subtend (form) an arc of a circle. That has an area of 2 x pi x r x (angle A) / 360.