Monday, March 8, 2010

Marielle's Growing Post

Rectangular Prism

the formula you have to use to find the total surface area of a rectangular prism is A=LxW .

For example if you have a rectangular prism with a height of 6cm, Length of 10cm and a width of 4cm. To calculate the total surface area of the rectangular prism you have to use the formula.

Front and back : 6cm x 10cm
A= l x w
A= 10 x 6
A= 60 cm
A= 60 x 2
A= 120cm

Top and bottom: 4cm x 10cm
A= l x w
A= 10 x 4
A= 40cm
A= 40 x 2
A= 80cm

ends: 4cm x 6cm
A= l x w
A= 6 x 4
A= 24cm
A= 24 x 2
A= 48cm

A rectangular prism has 6 sides therefore you have to times it by 2 because there are two sides of the same area.

To get the total surface area you. add it all together

TSA= (area of front and back) + (area of top and bottom) + (area of ends)
TSA= 120 + 80 + 48
TSA= 248cm2

Triangular Prism

to find out the total surface area of a triangular prism the formula you need is A=L x W & B x H/2

For example if you have a length of 10cm, base of 4cm and a height of 5 here's what you have to do, to get the total surface area.

A=L x H
A= 10 x 3
A= 30cm
A= 30x3
A= 90cm

You times this by three since there are 3 equal sides.

A=B x H/2
A= 5 x 3/2
A= 7.5cm
A=7.5 x 2
A= 15cm

You times this by two because there are two sides of a triangle.

Now to get the total surface area you have to add these together.

TSA= (3 x area of a rectangle)+(2 x area of a triangle)
TSA= 90cm + 15cm
TSA= 105cm2

Cylnder

to find out the total surface area of a cylinder you have to use the formula R= d/2, A= L x W and C= pi x r x r

For example if you have a cylinder with a diameter of 2cm and the length being 15 cm. To find the total surface area you'll have to do this ..

R= d/2
R= 2/1
R= 1cm

C= pi x d
C= 3.14 x 2
C= 6.28 cm

A= pi x r x r
A= 3.14 x 1 x 1
A= 3.14
A= 3.14 x 2
A= 6.28

You times it by two because there are two circles. One end and the other.

A= L x W
A= 15 x 6.28
A= 94.2cm

TSA= (area of the circles x 2) + (area of the rectangle)
TSA= 3.14 + 3.14 + 94.2
TSA=100.48cm2

How to find the surface area of a rectangular prism.

http://www.ustream.tv/recorded/5160006