How to Find Perimeter of Semi Circle

Video Transcript

"So how do find the perimeter or circumference of a semi circle? Hi, I'm, Jimmy and we're here to explore that right now. Well, if you know how to find the perimeter or circumference of a circle, then you'll know how to find the perimeter or circumference of a semi circle. You may have noticed I use the word perimeter and circumference in the same context, because in circle terms, they are one in the same. But circumference is used more widely in math. So, it all starts with the circumference of a circle which is C equals two pi r. Now, a semi circle by definition is that of a half circle. So, if a semi circle is a half circle, then the circumference of a semi circle, you just take the formula, two pi r, and divide that by two. Or multiply by half. And what ends up happening, is that the twos will cancel, so you're left with pi r. So the formula for the circumference of a semi circle is pi times r which is the radius of the original circle. So let's just say you are given that the radius of a circle was, let's just say, seven. Then, all you would need to do is plug in seven, where the r is, and so you'll have pi times seven, or, as more widely written, seven pi. Remember, pi is a number that's close to three point one four. Now, suppose you were given the diameter of a circle. Let's just say that the distance from one end of the circle to the other is, let's just say, twelve. Well, if the diameter is stretching all the way across the circle, then the radius has to be half of twelve, which in this case of course, is six. What you would need to do then is plug in the six into the circumference of a semicircle, so it will be pi times six, which is six pi. So, I'm Jimmy, and that's how you find the perimeter of a semicircle."