00:01
All right, two problems here, kind of like this one.
00:02
So it gives us a whole bunch of information about this pyramid.
00:06
It's growing, but it always stays a pyramid.
00:09
The key is knowing that the length of the side over h is going to always equal square to two over one.
00:20
That's an important piece that we need because it means a is equal to the square to two times h.
00:32
Okay, so we're going to need this.
00:34
It's an important piece.
00:38
Okay.
00:39
We got our volume formula for a pyramid.
00:42
This is important.
00:45
And what we want to find, it says, how fast is the height increasing? we want to find dh over dt.
00:53
This is so we want to find d .h.
00:58
Over dt.
00:58
Well, what we want to do is first use this guy to put everything in terms of h.
01:04
So our volume is going to be squared of 2 times h squared times h over 3.
01:13
And now here's what i'm going to start doing some math.
01:16
So my volume is 2h cubed over 3.
01:21
Okay.
01:22
And this is nice because now i can put, i can put the, i take the derivative.
01:32
So take the derivative with respect to t, d, v, over.
01:35
D t is equal to 6h squared over 3 times d h over d t and remember d h over d t is what we're looking for we can clean this up dv over d t equals 2 h squared times d h over d t and now we just got to put our numbers in okay it's saying the crystal is growing at a constant rate of 0 .5 centimeters cube that's our dv d t that's this guy.
02:08
0 .5 centimeters cubed growing, so it's positive.
02:13
It says at a particular point, the height is one.
02:18
Inside the ratio, it says how fast is the height increasing at this particular point? so when the height is one, i can go 2 times 1 squared times dh over dt.
02:31
Well, two times one squared.
02:33
This right here is just two.
02:34
So i just have to take the centimeter squared.
02:44
I like to put the units.
02:46
So i'm squaring.
02:49
Remember this is one centimeters.
02:55
And we're squaring this thing.
02:57
So the centimeters get squared.
03:00
It's just two centimeters squared...