Question

Perimeter of
semicircle?
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Answer 1

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.

Answer 2

semicircle is the half of the full circle

perimeter of the full circle is 2 π r .