Question

What is the area of a semi circle

Answer 1

The area of a whole circle is (pi) (radius²) .

So the area of half of it would be  (1/2) (pi) (radius²) .

If you don't know the radius, then you can use the formula     

                           Area = (1/8) (pi) (diameter²) .

Answer 2

You just find the area of a circle then divide it by 2
Area = Radius × Radius × $\frac{22}{7}$ (or pi)
Then divide your area by 2 and you get the semi-circle's area.