Math help :)

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Neche

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Hey guys, I'm reviewing for a discrete mathematics final coming up and just in review I found a question that's stumping my logic. If you could help it'd be great

for all sets A,B,C,D, (A x B) U (C x D) 'is a subset of' (A U C) x (B U D)
for all sets A,B,C,D, (A U C) x (B U D) 'is a subset of' (A x B) U (C x D)

One is true and one is false. I can't think of a counter example to either.

For the first, if A x B and C x D have similar element, say (x,y), then A U C must have x and B U D must have y, and a subset of that must have (x,y) in it. So it has to be true.

Now it doesn't specify unique elements, so I can say that, (x,y) == (y,x). BUT I'm not sure if that is the way to justify it or if there is another answer.

For the second, if A U C has an element x, and B U D has an element y, then A x B has (x,y). and C x D has (x,y) therefore it's true.

So which of my thoughts is wrong?

Thanks in advance
 
Don't listen to me lol, it's a Hitchhikers guide to the Galaxy joke. Was hoping someone would get it.
 
Life the universe and everything!


I got it Myrrh :p

My advanced math has more than a decade of rust on it, but I go with the first one being true....
 
!!!!!!! I got it to you jerks :( It was a sarcastic consideration !!!!

Maybe I'll make a computer that can make a computer to help me :(

I'm fairly sure that I can say (x,y) == (y,x), it's not a huge deal only a practice question.
 
The first is true.

(A U C)={a1,a2,a3,....,c1,c2,c3,....}
(B U D)={b1,b2,b3,....,d1,d2,d3,....}
Cross Product those and what you end up getting is (AxB) U (AxD) U (CxB) U (CxD).

(This shows the Distributive property of cross product: (A U C)x(B U D)=(Ax(B U D))U(Cx(B U D))=(AxB) U (AxD) U (CxB) U (CxD))

(A x B) U (C x D) is a subset of (AxB) U (AxD) U (CxB) U (CxD)!

If that doesn't make sense let me know :)
 
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Problems like this make me so happy I stopped going further and math and stuck with accounting. :S
 
What's really sad to me is that I remember being able to do this, but I can't anymore. Math is one of those things that if you don't use it, you lose it. :(
 
Celvantes said:
What's really sad to me is that I remember being able to do this, but I can't anymore. Math is one of those things that if you don't use it, you lose it. :(
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Yeah, I did discreet mathematics a couple of years ago, but I don't remember how to solve the above problem, because you don't frequently use that type of math =/

Tbh, it doesn't only go with math though. It goes with all kinds of knowledge. The difference is that with math, if you forget one part of something, you forget how to solve a whole range of problems. With, say, history, if you forget one detail, you'll likely still remember the context.

The good part, though, is that once you learn something, even if you don't remember 10 years from now, it is much easier to reobtain said knowledge. You still have it, its just locked away. So a bit of practice and its good as new.

Still, it makes me frustrated at times when I think "Oh, I did that in school" the few times when you actually might NEED something like that, but can't for the life of you remember how to do it. Its kind of like those times when you temporarily forget a word and get extremely annoyed because you know that you know the word, you just can't recall it.
 
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My brain hurts... :(
 
I'm in school for programming and it is a required course.
The logic behind it helps very much, especially with sets like what this question is dealing with. Of course it would be different things that are relevant to the product.

I just had it in my mind that U ' union ' meant intersection instead. I'm just crazy :(
 
Neche said:
I'm in school for programming and it is a required course.
The logic behind it helps very much, especially with sets like what this question is dealing with. Of course it would be different things that are relevant to the product.

I just had it in my mind that U ' union ' meant intersection instead. I'm just crazy :(
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Yes, I know. I had to take the course when I took programming as well.

Still, most of that course was rather useless imo. Sure, it helps putting you in the right way of thinking for programming, but if you already have it, the course isn't as helpful.
 
Uzor said:
Yeah, I did discreet mathematics a couple of years ago, but I don't remember how to solve the above problem, because you don't frequently use that type of math =/

Tbh, it doesn't only go with math though. It goes with all kinds of knowledge. The difference is that with math, if you forget one part of something, you forget how to solve a whole range of problems. With, say, history, if you forget one detail, you'll likely still remember the context.

The good part, though, is that once you learn something, even if you don't remember 10 years from now, it is much easier to reobtain said knowledge. You still have it, its just locked away. So a bit of practice and its good as new.

Still, it makes me frustrated at times when I think "Oh, I did that in school" the few times when you actually might NEED something like that, but can't for the life of you remember how to do it. Its kind of like those times when you temporarily forget a word and get extremely annoyed because you know that you know the word, you just can't recall it.
Click to expand...

I know the exact feeling. Maths is one of the things I hated in school but love now. Often, though, I see a problem I did the year before I left, and think "Hey, I did that, I can do that!", then I try and do it...and there's one part of the procedure I forget. Frustrating, but I usually go online to find out how it was I used to do it. For some weird obscure reason, Mathematics gives me great pleasure, and I feel a little strange for saying that. Enjoying algebra I can understand, because there's a distinct feeling of completion when you get your answer (so long as it has a numerical value). This is true for most Maths, I feel, as opposed to English or a similar subject, where opinions and context come in to play. With most Maths, you're either right or wrong, and I love that.
 
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