Video and Examples
Finding the perimeter of semicircles using the formula .
What is the perimeter of a semicircle with a diameter of 8cm? 
To answer this question, we need to realize that the figure is just half of a circle. This means we will still be using the formula . However, there will be a twist in what we do, because the formula gives us the circumference of a complete circle.
You will solve this problem using three steps: find the circumference of a full circle with the same diameter, divide that circumference in half, and then add the diameter.
Example 1 What is the perimeter of a semicircle with a diameter of 8cm? 

Step 1: Find the circumference of the full circle.


Step 2: Divide the circumference in half.
This is the length of just the curvy part of the semicircle. 

Step 3: Add the diameter. 12.56 + 8 = 20.56 cm This is the perimeter of the semicircle! 

Example 2 Find the perimeter of this quarter circle. 
Example 3 A wire is bent to form three semicircles. Find the length of the wire in terms of . 

Semicircle circumference – CLASSWORK
Solve each of the following problems.
Find the perimeter of this shape. 

Find the perimeter of this shape. 

SelfCheck
Question 1
A rope is arranged to form two semicircles as shown. Find the length of the rope in terms of π.

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Question 2 A garden is in the shape of a quarter circle. Find its perimeter.

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Question 3 A circle is drawn inside a square. Find the circumference of the circle.

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