Have you ever wondered How much cardboard does
Have you ever wondered? How much cardboard does it take to make a cereal box?
Surface Area- the sum of the areas of all the faces
Do you see the RED face? 4 in. 10 in. What are the dimensions of this rectangle?
Do you see another face that is just like the RED face? Where is it located?
Yes, it’s on the back. The front is a face. It is identical to the back. 4 in. 10 in.
40 in 2 2 The area of the front is 40 in². That means the area of the back is also 40 in².
4 in. 7 in. Do you see the BLUE face? What are the dimensions of this rectangle?
Do you see another face that is just like the BLUE face? Where is it located?
The right side is a face. It is identical to the left side. 4 in. 7 in.
28 in 2 The area of the right side is 28 in². That means the area of the left side is also 28 in².
Do you see the GREEN face? 7 in. 10 in. What are the dimensions of this rectangle?
Do you see another face that is just like the GREEN face? Where is it located?
The top is identical to the bottom. 7 in. 10 in.
70 in 2 The area of the top is 70 in². That means the area of the bottom is also 70 in².
We just need to add all the areas of the sides together. To find the total surface area, you add ALL the areas. 40 in 2 2 28 in + + 40 in 70 in 2 2 + 28 in + 70 in 2 2
The total Surface Area for this rectangular prism is 40 + 28 + 70 = 276 in 2
It’s your turn to try one!
Find the surface area. 2 cm 3 cm Area of top and bottom: 6 cm 3 cm x 2 cm = 6 cm 2 Since there are two of these shapes, 6 cm x 2 = 12 cm 2
Find the surface area. 2 cm 3 cm Area of front and back: 6 cm 3 cm x 6 cm = 18 cm 2 Since there are two of these shapes, 2 18 cm x 2 = 36 cm 2
Find the surface area. 2 cm 3 cm Area of both sides: 6 cm x 2 cm = 12 cm 2 Since there are two of these shapes, 2 12 cm x 2 = 24 2 cm
Find the surface area. 2 cm 3 cm Now add up the answers 6 cm 12 2 cm 36 2 cm +24 2 cm 72 cm 2
Formula for Surface Area of Rectangular Prisms length height width SA = 2(lw) + 2(lh) + 2(wh)
Formula for Surface Area of a Cube side Since all dimensions of a cube are the same, you only need to know the length of one side. SA = side 2 6(s )
How about another method?
Notes for your binder: S. Area: OTHER METHODS 1) “Football” Method 2) “Butt” Method
“Butt” Method 9 in 5 in 2 in
“Butt” Method 3 in 5 in 10 in
“Football” Method 3 in 2 in 10 in
“Football” Method 8 in 4 in 5 in
You try this one! Use whichever method you prefer… 4 cm 2 cm 6 cm
- Slides: 31