CIRCLES

 a geometric shape

What is a Circle?

Okay, so everyone should know what circles are, right? I mean, we all learn what they are when we're little kids. But my page are for those people who have short term memory loss and forgot what circles are and how to find the circumferece, area, etc. of them. So I guess I'll start off with the definition:

cir·cle -noun

"1. a closed plane curve consisting of all points at a given distance from a point within it called the center.

 2. the portion of a plane bounded by such a curve."

Definition from www.dictionary.com.

You can also say...

"A circle is a geometric shape - a set of points - consisting of points equidistant from a given point, the center of the circle. The common distance of the points on the circle to its distance is called the radius of the circle."

Taken from www.cut-the-knot.org.

What are Some Parts to a Circle?

There are three main parts of a circle. There is the radius, the diameter, and the circumference.The circumference is the outer boundary of a circle, or the perimeter. The diameter is the length across the center of the circle. To learn more about diameter, go to Unis's page on diameter. Lastly is the radius, which is equal to half the diameter. The radius is the length from the center of the circle to the edge.

 How do I find the Circumference of a Circle?

The circumference of a circle is the outer boundery of a circle. You can think of it as the perimeter of a circle. To find the circumference of a circle, you multiply pi (3.14) by the diameter.. The formula is C=3.14*d. How about I just put it in a couple of simple steps for you?

1. Measure the length of the diameter(d).

2. Multiply the length of the diameter by pi (d*3.14)

And then you're done! Mmhmm, it's that simple.

Here, I'll make your life easier and give you an example. Say the diameter of your circle is 7 inches. You would then multiply 7 by 3.14(7*3.14) and then you would get 21.98. So the circumference of your circle is 21.98 inches.

For more instructions, you can go to Caroline's page on circumference.

How do I find the Area of a Circle?

It's very easy to find the area of a circle. The area of a circle is the space inside a circle. To find the area of a circle, all you need to do is multiply pi by the square of the radius. The formula for that is A=3.14*r². There are two simple steps to finding the area.

1. Measure the length of the radius. (The radius is equal to half the diameter.)

2. Multiply the square of the radius by pi (r²*3.14)

And you're done! But you have to remember that the square of the radius is just the radius squared.

Here's an example. So the diameter of your circle is 7 inches. Then the radius of your circle would be 3.5 inches, right? Right. So then you multiply 3.14 by 3.5² (3.14*3.5*3.5). It's that simple. Simpler than you thought, huh?

What are Circles Used For?

You're probably thinking, "Circles are worthless. They're just a shape. What can I use them for?" But I say,"Heck no." Circles can be used for many things. Circles are the shapes of pies and pizzas, bagels and basketballs, but they can be used for math too. Take, for example, a circle graph. Those circles are used to graph things in basic slices. You can look at Wesley's page about circle graphs to learn more about circle graphs.

Practice Problems

 Okay. So I'm gonna give you some measurements and you have to figure out the area or the circumference.

1. Find the circumference when the diameter=21 inches.

2. Find the area when the radius=4 inches.

Were those too easy for you? Then here are a couple more challenging ones.

3. Find the circumference when the radius is 7 inches.

4. Find the circumference when the radius is 56 inches.

5. Find the area when the diameter is 64 inches.

6. Find the area when the diameter is 84 inches.

7. If the circumference is 86 inches, then how long is the diameter?

8. If the circumference is 75 inches, then how long is the diameter?

Are you answers correct? Is that your final answer? If you're doubting yourself, then here's the answers so you can correct them.

1. 65.94 inches

2. 50.24 inches

3. 43.96 inches

4. 351.68 inches

5. 3215.36 inches

6. 5538.96 inches

7. about 27.39 inches

8. about 23.89 inches

My Sources

I got my information from a number of sources. Here are some links so you can learn more.

1. From AAA Math, I found my information on area and circumference.

2. From Unis's page, I got my information on diameter.

3. I found my information of circle graphs from Wesley's page.

Well.....

I hoped you learned a lot from my page. I did work hard on it, and I hope you liked it. Don't forget to look at other people's pages because they're super duper good.