If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:3:47

Counting faces and edges of 3D shapes

Video transcript

how many faces does the following shape have pause this video and see if you can figure that out alright I'm assuming you paused and I'll see if we can work through it together and I'm going to actually try to color the faces so we have this space over whoops let me do it in my this other tool so you have this face over here in the back so that's one face so that's one then you have this face right over here also in the back the only way we can see this is because they've drawn it so that it is transparent so that is the second face now you have this triangular face on top so let me color that in so you have this triangular face on top so that's going to be our third face third face and then you have this triangular face on the bottom that's going to be our fourth face then it's going to be our fourth face so the key question is are we done looks like I've colored all the ones that I can see but this is one a little bit tricky here there's the one that we are actually seeing through there's the face there's we pick a color there's the face out front that we can see through so that we can see faces one two and four so that's actually going to be our fifth face the way they've drawn it it's like it's made out of glass so we can see faces one two and four but that is our fifth face and so this thing has five faces alright let's do another example but instead of faces that's going to think about we're going to think about edges so how many edges does the following shape have pause the video and see if you can work through this okay let's work through this together now and I'm just going to count these edges so the edges are where two faces meet so this is an edge right over there so that's one edge there's an edge back here we can see because it's transparent that is our second edge we have this one over here that is our third edge we have this one over there that is our fourth edge and we have this one over here that is our fifth edge now we have this here this is our sixth edge let's see all we have left is this one which is edge number seven and then last but not least this edge over here which is edge number eight and I actually found it's very valuable to color them in to make sure that I wasn't missing an edge or double-counting an edge so this thing has eight eight edges actually if you're curious this were extra practice how many faces does this have well we can count those as well this has one face back there another face back there so it's two faces and then you have a third face which is the base this rectangular face so that's three faces and then you have your two faces out front you have this face that we're seeing through and then we have that face that we're seeing through so even though they're asking edges just for practice we figured out that this thing has five faces one for the square base and then four triangular faces for these sides to make this to make this square pyramid so it has eight edges and five faces