00:01
Okay, so we're creating a standing wave from these two functions.
00:04
So what we do is we add them together.
00:14
I'm going to not put in all the units.
00:36
Okay, then i'm going to use the usual identities for the sum and difference, sine of the sum and difference.
01:58
And if we look at that, we can see that two of the terms are going to cancel out, which are these two.
02:07
So this is equal to 12, because there's two of those terms, times sine of pi x cosine 400 pi t.
02:29
So for parts a, b, and c, we want the nodes.
02:35
So the nodes happen when sine of pi x is equal to zero, so that x is equal to some integer times pi.
02:50
Well, the one at x equals zero does count.
02:55
So those are our three smallest values of x where we have a node.
03:29
So we get our period like this.
03:30
That's from the argument of the cosine term.
03:40
So the wavelength is 2 pi, and the period is, from the argument of the x part, we have that pi x is equal to kx, which is 2 pi over lambda x...