1
00:00:00;00 --> 00:00:05;03
So, think rate of change
as it relates to vertex.

2
00:00:11;13 --> 00:00:14;00
[I know what X is
when Y is zero]

3
00:00:14;01 --> 00:00:18;03
OK, how come? That's what
you just said. Find out

4
00:00:18;04 --> 00:00:19;08
what X is, when Y is 0.

5
00:00:19;09 --> 00:00:21;06
That's when you
plug in 0, but how come?

6
00:00:22;14 --> 00:00:26;11
That's the vertex when it
turns around from negative

7
00:00:26;12 --> 00:00:29;11
to positive. From
positive to negative.

8
00:00:29;12 --> 00:00:32;12
Alright then. You just answered all your own

9
00:00:32;13 --> 00:00:37;11
questions. That's why you
set it to zero. Because all

10
00:00:37;12 --> 00:00:40;11
the way prior to this point
what's the rate of change?

11
00:00:40;12 --> 00:00:41;05
[Negative]

12
00:00:41;06 --> 00:00:42;08
So, what would
your curve be doing?

13
00:00:42;09 --> 00:00:44;01
[Decreasing]

14
00:00:44;02 --> 00:00:47;06
OK. Anything beyond this
point to the right of the X

15
00:00:47;07 --> 00:00:49;00
value too, what's
your rate of change?

16
00:00:49;01 --> 00:00:49;09
[Positive]

17
00:00:49;10 --> 00:00:50;10
So, what would
your curve be doing?

18
00:00:50;11 --> 00:00:51;06
[Increase]

19
00:00:51;07 --> 00:00:56;00
So, it's got to change. The
change happens when Y is?

20
00:00:56;01 --> 00:00:56;11
[Zero]

21
00:00:56;12 --> 00:00:59;05
Not negative, not
positive, but zero.