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Hi, in this video, i'm going to answer just number two.
00:04
So there are three problems listed here, but if you want all of them answered, you should ask them separately.
00:10
So i'm just going to do number two, and i hope that's one that you want.
00:16
So in this one, we have a probability density function with two random variables given by fxy is equal to alpha xy, when x and y are both in the range zero to one, and it's zero otherwise.
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So the first thing we want to do is determine the value of alpha, and we do this by using the fact that the probability density function must integrate to one.
00:51
In other words, the total probability of our space must be one, which is just saying that all the events that could possibly happen, must happen with probability 1.
01:04
So in terms of math, that's saying if we integrate over our space, which is from 0 to 1 for x, 0 to 1 for y, alpha xy, dx, y, this has to equal 1.
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So let's do this integral.
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So we have 0 to 1.
01:25
We have alpha x squared over 2y from 0 to 1, dy.
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So this comes out to just integral from 0 to 1, alpha y over 2, d, y, which is integral from 0 to 1.
01:47
Oh, wait, sorry.
01:49
Now we take the anti -derivative, and what do we get alpha y squared over 4, 0 to 1? so we just get alpha over 4, and this equals 1.
02:06
So we have alpha equals 4.
02:13
Now for b, we want to find the marginal probability of, well, i guess b and c, i'll just do it together, because they're essentially the same.
02:24
So b and c.
02:25
So first we'll start with the marginal probability for x.
02:30
And so in this one, all you do is you nail down in x, and then you integrate over all the possible y for that x...