Math Community Quiz

[jnesselr]

I think Nemo should get it. He got the correct answer first

Oh, I understand. Ninja'd once, ninja'd twice. ;-)

[nemo]

you guys want a really hard one? i came up with one but i don't even know where to begin to solve it.

[jnesselr]

you guys want a really hard one? i came up with one but i don't even know where to begin to solve it.

Do it. I need something to sleep on while I sleep.

[ruler501]

I need something to work on lets see how hard it is. Might help me sleep. I could use it then

[nemo]

ok. find the 2x2 matrix whose determinant equals the sum of the upper left hand corner and the bottom right hand corner. the matrix must be filled with prime numbers only.
to be clear:

Code: [Select]

[2  7]
[3  5]
the determinant is 2 * 5 - 3 * 7, or -11. the upper left hand corner is 2, and the lower right hand is 5. so if this was the winning matrix, 2 + 5 would have to equal 2 * 5 - 3 * 7.
2 * 5 - 3 * 7 is the determinant of that matrix. questions? ambiguities?

just to warn you, i have no idea if such a matrix exists or not. it's just a question i made up.

[ruler501]

The only real hard part about this should be the prime numbers The other part should be easy enough

[Runer112]

Code: [Select]

[2  1]
[1  3]

? Not sure if 1 counts as prime...

EDIT: Nevermind, 1 isn't prime. Anyways I remembered I need to be quiet for this question, I'm not allowed to answer.

[nemo]

Code: [Select]

[2  1]
[1  3]

? Not sure if 1 counts as prime...

oh, sorry. no 1 does not count.

edit: and i found a matrix. a lot of them, actually...
edit2: and any of them will be accepted.
edit3: yeah i found 242 matrices that work within the first 100 primes... so it's definitely doable.

[thepenguin77]

[5 7]
[7 7]

Edit: nvm, this is backwards.

[nemo]

penguin, that doesn't work because the determinant is negative 12 and 5+7 is positive 12.

[thepenguin77]

[7 7]
[5 7]

That's better.

Edit:
     I solved it right the first time, I just forgot what I was solving.

[nemo]

yeah, the penguin wins.

[97][19]
[5]  [2]
 

[ruler501]

[5 3]
[5 5] this and many other ones work just solve x^2-2x-Bx=0 with B being prime and look for prime zero's

Now I need a much harder problem to help me sleep.

EDIT: Shoot i was to late.

[nemo]

[5 3]
[5 5] this and many other ones work just solve x^2-2x-Bx=0 with B being prime and look for prime zero's

Now I need a much harder problem to help me sleep.

EDIT: Shoot i was to late.

same problem but with perfect numbers instead of prime numbers? that'll keep you up for a long time.

[thepenguin77]

Here is a tough one. I once attempted this and failed, but when I went online, I found out that I went about it wrong. But I still believe I did it the right way. The problem comes from http://xkcd.com/135/, problem 1. All I am saying is solve it.

Here's what you have to assume:
1. The person's speed is always 6 m/s.
2. The raptor's top speed is a mathematical limit, not just a point at which it stops accelerating. Meaning that its recursive forumula is V[n] = V[n-1] + 4 - (4V[n-1]/25).
3. Even if this isn't the proper way to solve it, this is the way I say to do it.

At this point, I don't know the answer, but if you show some meaningful work, I'll have to believe it.