00:01
So if you want to look at this pipe and it has an outer radius and i can't see your diagram so i'm going to assume that this is what your picture looks like and there's an outer radius and an inner radius and again this would be kind of hidden see this back here and so the inner radius is r the outer radius is capital r and then the length of this is h.
00:33
And so if i want to find the volume of this, i find the volume by taking for a cylinder.
00:40
I take pi times the radius squared times how long it is.
00:46
So the area of a cross section.
00:48
And that would be this entire circle.
00:51
So this would be the volume of the, if it was solid.
00:57
Now we need to subtract away that inner solid.
01:03
So this is the big solid, big solid, or big cylinder, minus the inner solid cylinder.
01:20
And so the inner solid cylinder is going to be that pi times the small radius squared times h.
01:30
So now what they're doing is saying another way to do this, and this kind of is a lead -in to calculus.
01:36
Another idea is to take and cut this guy down and lay it out flat...