00:01
So we want to find the volume when we rotate around the y -axis.
00:04
And our functions are y -equals x squared, x -equals 0, and x -equals 3.
00:12
Now, i'm interpreting this question.
00:14
I'm not seeing the book.
00:15
I'm interpreting this question as here's our y - equals x -squared, and we're having x -equal -0, so we're only using basically in this first quadrant, and x -equals 3.
00:27
So x -equals 3 would come up here, this and intersect at that point of three and nine.
00:34
And so i believe this is the region that they're discussing.
00:37
I would have more likely had said that y equals zero is the other bounding mark.
00:43
However, i didn't write the book.
00:46
So if we rotate that around the y axis, that's going to come over here.
00:51
And then we can use either a shell method or a disk method.
00:56
And why don't we use the washer method? so if we have one washer, the exterior of the washer is here, and that interior of the washer is here.
01:07
And it's going to have a thickness that is only d .y.
01:10
So we'll have to write the uniferal in terms of y.
01:13
And so we will need this function solved for x, and that would be x equals the square root of y.
01:21
So we can think of any point along here.
01:24
If we take just a random point along here, it has a particular x coordinate of square root.
01:30
Root of y...