First off!!! What is a circle??
A circle is a round flat shape whose edge is at the same distance from the centre all the way around.
Now, let's move on to the basics!
Circumference is the distance around a circle. To find the circumference, you use a formula, d*pi or if the diameter is not given, you use the radius, and the formula would be r*2*pi.
Diameter is goes through the center of the circle. It's basically half of the circle.
Radius is any point on the circle that starts at the center to the edge of the circle. It's half of the diameter. That's why you multiply the radius by 2 if the diameter is not given.
Pi is a decimal that is used in calculating the circumference and area of the circle. It's shorten to be known as 3.14
Here are some examples:
The radius of a circle is 8cm long. Find the circumference.
Well all there is to do is multiply 8 by 2 because the formula is d*pi. So, 8*2 = 16 and 16 times 3.14 equals 50.24. This means the circumference of the circle is 50.24cm.
Ok let's say the diameter is given now and the diameter is 12cm long. What is the circumference?? Well, all you do is simply just multiply 12 by pi (3.14 to make things simple) and you get 37.68. So the circumference is 37.68cm. JUST THAT SIMPLE!!!
Now that we've talked about the circumference of a circle, let's go on to the area of a circle!!!
The area of a circle is the number of square units inside the circle.
To find the area of a circle, there's of course a formula! The formula is radius squared times pi. So, instead of multiplying the radius by 2, you square the radius, which means multiply the radius by itself and then by 3.14.
For example:
Let's say the radius of a circle is 5in. long, and you were asked to find the area. What you have to do is square the radius, which means you multiply 5 by 5 and then you multiply it by pi. So, 5*5 is 10 and 10 times 3.14 is 31.4. The area of the circle is 31.4in. squared.
Anytime you find the area of any shape, you have to square the result because you are multiplying two measurements. You don't square the circumference because you're just finding the distance around the circle.
If you were asked to find the area of a circle, but the diameter is the only one given and you know in area of a circle, you don't need the diameter, only the radius, it's pretty easy what to do.
For example:
The diameter of a circle is 19in. long. They ask you to find the area. Well, all you is divide 19 by 2 because as I said before, the diameter is twice as much as the radius. So, 19 divided by 2 is 9.5. Then, you multiply by pi. So, 9.5*3.14 = 29.83 and the area of the circle is 29.83in. squared.
Now let's see what 3D shape has circles......CYLINDER!!!!
Let's say the height of a cylinder is 28cm long and the radius is 15cm long. What is the volume of the cylinder?? Now recognize that I said volume. When dealing with 3D shape, you use volume, which is the amount of space occupied by something or enclosed within a container. Your result should always be in cubic because its 3 dimensional.
Basically, all you have to do is first find the area of the circle. So, 15*15*3.14 = 706.5. After you find the area of the circle, you multiply it by the height, which in this case is 28. So, 706.5*28 = 19782. The volume of the cylinder is 19782 cubic cm.
WHEW!!! AND.....WE'RE DONE!!! Our brains have been busy, now it's time to give it a massage!!! Anyway, hope this help you know about our world of CIRCLES!!!!
