Math Is Fun Forum

  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

You are not logged in.

#1601 This is Cool » vector multiplicated by i » 2005-12-17 08:57:41

krassi_holmz
Replies: 11

What will happen with the vector if we multiply it by

?

#1602 Re: Help Me ! » Factorising quadratics... again » 2005-12-17 08:48:36

Here's another question-when the
ax^2 + by^2 + cxy + dx + ey + f
is factorisible?
Here's an example:
3x^2+5y^2+2xy+7x+9y+10(not factorisible)

Is there a method such for this task?

#1603 Re: Help Me ! » Factorising quadratics... again » 2005-12-17 08:41:32

Here is it:
Let
F[x]=ax^2+bx+c and F[x] is not factorisible.
Proof that in the rank
F[1], F[2], ...
exist infinitely many prime numbers.

#1604 Re: Help Me ! » Solving infinite series » 2005-12-17 08:29:38

And what did everybody draw from this lesson?
was here anything else posted? I don't think so. smile wink smile

[Yes. Yes there was. *points to 'last edited by...' tag*]

#1607 Re: Help Me ! » Solving infinite series » 2005-12-17 08:06:55

Why are we disputing something fundamental?

#1608 Re: Guestbook » Male vs. Female injuiry » 2005-12-17 07:53:38

I think exactly the same. We'll see.

#1609 Re: Help Me ! » Factorising quadratics... again » 2005-12-17 07:44:28

Merry Christmas Ricky and Mathsy!





I have a problem:
What picture is better than e^Pii?
This is e^Pii with christmas hat on e! smile
But when I try to change my picture, I get the message that the picture has been refreshed and then I go back. But then I see my previous picture. Has anybody had the same problem as mine?

#1610 Re: Help Me ! » Factorising quadratics... again » 2005-12-17 07:35:58

Yes, your method is truely better in a ways.

#1612 Re: Puzzles and Games » Magic square computation » 2005-12-17 07:23:46

And interesting hard task:
Prove that there dosen't exist magic square of non-serial fibbonachi numbers.
smile

#1613 Re: Help Me ! » Solving infinite series » 2005-12-17 07:15:24

2+4+8= (8-1)/(2-1) or 2+4+8=2(8-1)/(2-1), e.a
14=7 or 14=14?

I'm sure that


Why first x in the numerator shouldn't be there?

#1614 Re: Help Me ! » Factorising quadratics... again » 2005-12-17 07:02:55

You can (what is the word for taking divisor out of brackets),so
-2x^2 - 3x + 2 =
=-(2x^2 + 3x - 2)=
=-2(x^2+3/2x-2/2)=
=-2(x^2+2.(3/4)x+-(3/4)^2-1)=
=-2((x+3/4)^2-(1+9/16))=
=-2((x+3/4)^2-25/16)=
=-2((x+3/4)^2-(5/4)^2)=
=-2(x+3/4-5/4)(x+3/4+5/4)=
=-2(x-1/2)(x+2)=
=-(2x-1)(x+2)=
= (x+2)(1-2x).

#1615 Re: Guestbook » Male vs. Female injuiry » 2005-12-17 06:21:50

For now the injuiry only proofs that the mathematics theory is correct.
The males must be statisticaly equal to the females.

#1616 Re: Help Me ! » What does this notation mean? » 2005-12-17 06:16:52

Tell us where is it from.
So it may be

#1619 Re: Help Me ! » Linear Programming » 2005-12-17 04:32:44

The question isn't so hard but there are a lot of things to consider.

#1620 Re: Help Me ! » Really need to simplify some horridly complex ecpressions » 2005-12-17 04:12:11

I've simplifed mathisfun's equation, but very little.

#1621 Re: Help Me ! » Solving infinite series » 2005-12-17 00:18:42

Sorry, if I made a mistake, but I think:






But
, so

and

Thus we have:
S=7(1-1/2-1/4)-(1/4-1/5-1/25)=7/4 - 1/100 = 87/50 = 1,74

#1622 Re: Help Me ! » Really need to simplify some horridly complex ecpressions » 2005-12-16 21:55:03

Yes, I think this forum is better than any  simplification software smile

#1623 Re: Help Me ! » Another Question Via Email » 2005-12-16 21:28:46

When I think for a while, I found an interesting fact:
The question is
Which remainders by K suppose that p is eventually prime?
So, if  tru
If a number is from the form


if GCD[K,G]>1 then L is truely non-prime.
So, if all prime, greater than K are from the form

then for all 1<i<K-1 GCD[i,K]>1
Let find the chain of K-s
The firs member is 4:
GCD[4,2]=2
The second is 6:
GCD[6,2]=2
GCD[6,3]=3
GCD[6,4]=2
Is there third?
I think there isn't.
Here's what have to be prooved:
There isn't number H greater than 6 for such every prime numbers, greater or equal to H-1 are from the form

#1624 Re: Help Me ! » Another Question Via Email » 2005-12-16 21:08:50

All the prime numbers greater than 3 are from the type


and from the type

#1625 Re: Jai Ganesh's Puzzles » Problems and Solutions » 2005-12-16 20:58:20

I think Ricky is right. Here's a direct proof:
Let
u^2-v^2 = p
We'll find u and v by p:
u^2-v^2 = p
=> (u+v)(u-v) = p, but p is prime, so his divisors are only 1 and p, so:
u+v=p && u-v=1
=> u=v+1; 2v+1=p; v= (p-1)/2, but p is odd, so v is integer.
So:
v= (p-1)/2
u=1 + ((p-1)/2)= (p+1)/2.

Board footer

Powered by FluxBB