a) Find the area of a semi circle with diameter 12cm. b) The area of a semi-circle is 60cm^2. Find the radius of the sem-circle.

a) radius = 12/2 = 6cm. Area of a circle = pi x r^2 = 36pi. Area of semi-circle = 36pi / 2 = 18pi cm^2b) Area of full circle = 120. pi x r^2 = 120. r^2 = 120/pi. r = sqr root (120/pi)= 6.18cm