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## Grade 8 (Virginia)

### Course: Grade 8 (Virginia) > Unit 7

Lesson 3: Surface area- Surface area using a net: triangular prism
- Surface area using a net: rectangular prism
- Surface area of a box (cuboid)
- Surface area of a box using nets
- Surface area using nets
- Expressions to find surface area
- Surface area
- Surface area versus volume
- Surface area word problem example
- Surface area word problems
- Surface area review

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# Surface area using a net: triangular prism

Here are the steps to compute the surface area of a triangular prism: 1. Find the areas of each of the three rectangular faces, using the formula for the area of a rectangle: length x width. 2. Next, find the area of the two triangular faces, using the formula for the area of a triangle: 1/2 base x height. 3. Add the areas of all five faces together, and you're done!

## Want to join the conversation?

- At1:00How did he get 1/2(22 votes)
- Like i said to selion if your talking about how he got the 1/2, thats apart of the formula. Which is, Half of the base times the height, OR, Half the height times the base(21 votes)

- How many nets for a prism is there?(11 votes)
- There are in fact, 9 nets for a triangular prism you saw in Sal's video. Never can a prism or shape have 1 or less net.(2 votes)

- i need help on nets and surface area(10 votes)
- If you don't understand this, try going back to Unit 8 - Plane figures (if you haven't already done it, complete it before going back to this). You can also try the course called "Getting ready for 6th grade."

Here is how to find areas of different parts of nets:

The formula for a triangle is 1/2 times Base times Height.

The formula for a square is Base times Height.

The formula for a parallelogram is to break it into two smaller triangles, switch it around to make a square, and find Base times Height of the square.

The formula for any other shape is break into other shapes (triangles, squares, etc.), find the area for all the broken-up shapes, and add it all up.

Once you have found the area for all the parts of the net, add the parts together to find the area of a net.

Hope this helps!(3 votes)

- sooo i ahve a question to anyone who whould like too answer me....... HOW DO YOU DO THIS? im so lost its sad can yall please help!(4 votes)
- A= HB/2 (Half of the base times height, Thats the formula for a triangle, i dont have time to give you the other formulas but i hoped this helped.(6 votes)

- is there a better way to explain this like a talk through b/c is still dont understand.(6 votes)
- i have lost brain cells(6 votes)
- ikr its too confusing(1 vote)

- how come the video will not play(3 votes)
- It could be a few reasons, either your device that you are using is becoming old and it's breaking down, their could be one too many things connected to the internet or your internet sucks because of the internet provider that you are using isn't so good(1 vote)

- how do you know if you're placing the numbers correctly??(7 votes)
- this video make me have more questions...(5 votes)

## Video transcript

- What I want to do in this
video is get some practice finding surface areas of figures by opening them up into
what's called nets. And one way to think
about it is if you had a figure like this, and if
it was made out of cardboard, and if you were to cut it, if you were to cut it right
where I'm drawing this red, and also right over here
and right over there, and right over there and also in the back where you can't see just now, it would open up into something like this. So if you were to open it up, it would open up into something like this. And when you open it up, it's much easier to figure out the surface area. So the surface area of this figure, when we open that up,
we can just figure out the surface area of each of these regions. So let's think about it. So what's first of all the surface area, what's the surface area
of this, right over here? Well in the net, that
corresponds to this area, it's a triangle, it has a base
of 12 and height of eight. So this area right over
here is going to be one half times the base, so times 12, times the height, times eight. So this is the same
thing as six times eight, which is equal to 48 whatever
units, or square units. This is going to be units of area. So that's going to be 48 square units, and up here is the exact same thing. That's the exact same thing. You can't see it in this figure, but if it was transparent, if it was transparent,
it would be this backside right over here, but
that's also going to be 48. 48 square units. Now we can think about the areas of I guess you can consider
them to be the side panels. So that's a side panel right over there. It's 14 high and 10 wide,
this is the other side panel. It's also this length over here
is the same as this length. It's also 14 high and 10 wide. So this side panel is
this one right over here. And then you have one on the other side. And so the area of each of these 14 times 10, they are 140 square units. This one is also 140 square units. And then finally we
just have to figure out the area of I guess you can say the base of the figure, so this whole
region right over here, which is this area, which is
that area right over there. And that's going to be 12 by 14. So this area is 12 times 14,
which is equal to let's see. 12 times 12 is 144 plus another 24, so it's 168. So the total area is
going to be, let's see. If you add this one and
that one, you get 96. 96 square units. The two magenta, I guess
you can say, side panels, 140 plus 140, that's 280. 280. And then you have this
base that comes in at 168. We want it to be that same color. 168. One, 68. Add them all together, and
we get the surface area for the entire figure. And it was super valuable
to open it up into this net because we can make sure
we got all the sides. We didn't have to kinda
rotate it in our brains. Although you could do that as well. So, with six plus zero plus eight is 14. Regroup the one ten to the tens
place, there's now one ten. So one plus nine is ten, plus eight is 18, plus six is 24, and then you have two plus two plus one is five. So the surface area of this figure is 544. 544 square units.