What is the area of a 10cm semi circle?

Well, darling, a semicircle is half of a circle, so to find the area you just take the area of a full circle and divide it by 2. The formula for the area of a circle is πr^2, so for a 10cm semicircle, you'd calculate it as 0.5 * π * 5^2, which gives you an area of 39.27 square centimeters. Voilà!