Sparsh Thapa

Swift school     311

                       Circle

What is a circle?

A circle is a round plain figure
which has no edges.

The circle has a center which is the middle of the circle. The distance from the center to the edge of the circle

The diameter is the distance from one edge of the circle to another

The circumference of a circle is the distance around the circle. It can be found using pi*D

But what is pi?

Pi is the circumference divided by the diameter. For example if the circumference of a circle is 25.12 cm and the diameter is 8 we can find what the pi is C/D

                                                                                25.12/8

       pi= 3.14

The official value of pi is 3.14159265.. and it goes on forever but to make it simple 3.14 is used.

     

    Circumference of a Circle

The circumference of the circle it the distance around the circle. This can be found using a formula C=pi*D.

For example if D is 5 cm what is the circumference?

it can be found using C=pi*D

                                 C=3.14*5

                                C=15.7 cm

What if only the radius is given?

You multiply the radius by 2 and get the diameter.

For example

the radius is 5 what is the circumference

                C=pi*D

                C=3.14*(5*2)

                 C=3.14*10

                C=31.4 cm

The area of the circle is the amount of the space the 2D circle occupies. The area of the circle can be found using a simple formula which is A=pi*r2. The r is the radius which is also half other diameter. The radius is the distance from the center of the circle to the edge of the circle. The pi is 3.1

for example if we say that the radius is 5 cm. The area could be found using the formula A=pi*r2

A=3.14*5 squared

A=3.14*25

A=78.5 cm squared

The example goes through the steps used to find the circle. 1st the equation was written A=pi*r2. Then we substituted the variables with the known variables. We knew that radius was 5 cm and pi was 3.14 . After we did that we started with the exponents and 5 to the power 2 is 5*5=25 and the answer was 25. After we found the radius squared we multiplied it by 3.14 which is pi. 3.14*25=78.5 so the answer was 78.5 cm squared.

If we were given the diameter and told to find the area our first step wouldn't be A=pi*r2 because we don’t know the radius which is needed to find the area. A diameter is a distance from one edge of the circle to another.  

                                       

  Finding the surface area of a 3D object

The surface area of a 3D object can be done by adding all the areas of a shape

  

How can we find the area?

The circle can be broken into flat shapes

Now we can say the radius of the circles shown above is 5 cm

1st we find the area of one of the circle which is done by the following formula

       A=pi*r2

      A=3.14*(5)squared

      A= 3.14*25

     A=78.5 cm squared

now for the rectangle the length is 5 cm and base is 10 cm

    A=5*10

   A=50 cm squared

After that i knew we had two circles so i multiplied  78.5*2=157 cm squared

and after i did that i added the two circles area with the area of the rectangle 157 cm+50=207 cm squared