00:01
Into the y axis i'm just going to kind of jump into what's going on here is you have this this curve got x equals one and we're going to take all of these regions and we're going to rotate it using shells um and well i hope you can see it's the lateral area of a cylinder which is 2 pi r h so as i'm looking at this problem the first one so number one is going to be 2 pi and then the integral is from 0 to 1.
00:32
Those are my x values.
00:34
The radius of each one of these cylinders is x.
00:38
And the height is that 17x squared dx.
00:42
So if i were doing this problem, i would multiply be 17x cubed.
00:48
So if you take the anti -derivative of that, you have to add one to that exponent, and then you have to divide by your new exponent going from 0 to 1.
00:56
And please don't forget about that 2 pi in front.
00:59
And this is a very time.
01:00
Really nice because if you plug in one right there, one to any power is just one.
01:05
And so i'm going to end up with 17 pi.
01:09
And remember two goes into four twice.
01:12
And that'll be your final answer.
01:13
Now, i am plugging in zero, but it's plugging in zero is just going to give me minus zero.
01:17
So you don't have to write that down.
01:19
So the next one, i don't believe, is much different.
01:22
It's kind of set up the same way.
01:26
Except so because it's such a long problem, i'm just going to jump right into.
01:30
2 pi the bounds they give you are from 2 to 3 the radius is still x and the height of each one of these is 9 over x dx which is actually a really nice problem because these xes will cancel out and i can figure out the integral of 9 it's just 9x and do that from 2 to 3 just make sure you plug in your bounds so 3 times 9 is 27 2 times 9 is 18, which will give me 9, but i have to multiply by that 2 pi.
02:05
So it should be 18 pi...