00:01
Let's take the derivative first, okay, pi over 9 minus pi over 9 sine of pi x over 9, set it to 0, sine of pi x over 9, pi over 9 here, pi over 9 here, they go away, right, 1.
00:21
So sine of pi x over 9 is 1.
00:26
Where is sine 1? at pi over 2, 3 pi over 2, right, and 5 pi over 2, it goes like that, okay.
00:39
So then pi x over 9 is equal to pi over, pi over 2, let's start with that, then x is equal to, pi cancels out, 9 over 2, okay.
00:56
So let's see, because we are from 0 to 18, so 18 endpoints are 0 and 18, 9 over 2 is one of them, and what if we say pi x over 9 is equal to 3 pi over 2, so then this is going to be 9, and then this is going to be pi x over 9 is equal to 5 pi over 2, that's going to be 45 over 2, or that's going to be more than, okay, we're not going there.
01:45
Good, so this is the only, only, these are the only points we have, so let's see what we have.
01:50
I just noticed that, actually this is not 9, this is 27 over 2, which is right off, right before we, we leave the endpoint, so, so it's going to be 13 and a half, right? okay, when x is 0, what do you have? you have 1...