First, find the entire circumference of the whole circle which is: C=2πr. Then, divided the circumference with 2 to get the circumference of semi circle. Hope it help!
The perimeter of a circle is π × d where d is the diameter so half of that is 1/2 π × d. But If you are going to walk around a semicircle you need to go half way around the circle and then across a diagonal to get back to where you started so the perimeter is 1/2 π × d + d.
