00:01
Okay, this problem has a lot of questions regarding finding volume by rotating around an axis.
00:06
So we're just going to look at the first one where y is equal to 4 minus 12x, and we have the boundaries, y is equal to zero, and we're looking between x is equal to 2 and x is equal to 3, and we're rotating around the x axis.
00:19
So we are looking for this point, or this area, right, between x is equal to 2 and x is equal to 3, and we're going to be rotating around the x axis.
00:30
This will kind of give us a disk that's going to look something like this.
00:39
So that'll be kind of like our 3d shape that we're looking at here.
00:43
Now let's get rid of those lines just so we're not confusing ourselves here.
00:49
So here is the area that we're looking to rotate around our x -axis.
00:55
Now when we're rotating around the x -axis, we're going to think about our area in terms of x.
01:00
So our volume formula, we're going to use the integral between a and b.
01:05
Those are going to be our boundaries in this situation.
01:09
And we want the area of x.
01:11
Well, the area of x, just like any area of a disk, is going to be pi r squared where r is the radius.
01:19
Now, to find the radius in the situation, you're going to take your outer radius, which is going to be the outer.
01:25
If we kind of make a little example of where we're looking for our radius, from here, right? we're looking for where we are going to be rotating around the axis.
01:37
So we're looking at like what's our outer radius and we're going to subtract anything in our inner radius.
01:45
So the outside we can see is going to be bounded by our formula y is equal to 4 minus 12x and our inside is going to be bounded by the formula y is equal to zero.
01:58
That means our inner radius is going to be just zero in this situation...