00:01
All right, just to kind of over -explain this problem.
00:03
Since we are instructed to do the y -axis, and we are also instructed to do pi r of t squared minus lowercase r -of -t squared, d t, and a row from a to b, that is my clue that we're doing the washer method.
00:28
So in order to answer this question, man, that was terribly written method, is that your rectangles are going this way.
00:40
So the way i would answer this question is that, so it even says perpendicular to the y -axis.
00:48
So that first answer is horizontal.
00:56
So then when they ask you to find the value, oh, what should be the variables, x or y, everything is going to be in terms.
01:04
Terms of y.
01:05
So when they give you that equation, how do they write it? y equals 4 minus x squared.
01:15
What you're going to have to do is, well at least what i would do is add x squared to the left side and subtract y to the right side.
01:24
And then you would square root.
01:26
And we only need the positive version of the square root because we're in quadrant one.
01:33
So then what's the lower integrate into limit of the integration, that's actually asking for this value here...