## Video and Examples

Finding the perimeter of semi-circles using the formula $\large~P\,=\,\frac{\pi~d}{2}\,+\,d$.

 What is the perimeter of a semi-circle 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 semi-circle 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 semi-circle. Step 3: Add the diameter. 12.56 + 8 = 20.56 cm This is the perimeter of the semi-circle!

 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 .

# Semi-circle circumference – CLASSWORK

Solve each of the following problems.

 Find the perimeter of this shape. Find the perimeter of this shape.

# Self-Check

 Question 1   A rope is arranged to form two semi-circles as shown. Find the length of the rope in terms of π. [show answer]

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

 Question 3 A circle is drawn inside a square. Find the circumference of the circle. [show answer]