## Search found 151 matches

Mon Mar 28, 2011 8:26 pm
Forum: Higher Secondary Level
Topic: minimum products needed
Replies: 0
Views: 1019

### minimum products needed

Consider a sequence of $n$ nonzero numbers where at least one of them is positive. You are not allowed to see the numbers, but can know the sign of product of any two. Find, with proof, the minimum number of products you need to know if you want to determine the sign of every number in that sequence.
Wed Mar 23, 2011 12:27 am
Forum: College / University Level
Topic: Injection from R2 to R
Replies: 4
Views: 6279

### Re: Injection from R2 to R

There's one that maps all the points in $(0,1) \times (0,1)$ to $(0,1)$. Take $(0.a_1a_2a_3 ... ,0.b_1b_2b_3 ...) \rightarrow 0.a_1b_1a_2b_2a_3b_3...$. Such a map should work also
Tue Feb 15, 2011 11:19 pm
Forum: Physics
Topic: simple pendulam in vacuam
Replies: 3
Views: 1749

### Re: simple pendulam in vacuam

Motion of a simple pendulum is governed by gravity. So there is no reason that it will not oscillate in vacuum
Mon Feb 14, 2011 2:16 pm
Forum: Number Theory
Topic: An easy to prove result about squares
Replies: 1
Views: 1133

### An easy to prove result about squares

There are infinitely many non palidromic squares so that their digit-inverse (number formed by reading the number right to left) is also a square.

The result is wordy but the proof is verrrrry easy
Sun Feb 13, 2011 11:45 pm
Topic: BdMO National Secondary (Higher Secondary) 2011/7
Replies: 8
Views: 3648

### Re: BdMO National Secondary (Higher Secondary) 2011/7

Fahim, your strange proof is correct.
However, you should note one thing here (though I'm sure you are just good enough at recognizing it). For the completeness of the proof, you should also prove that friend of enemy and enemy of friend is an enemy. It seems trivial, but necessary.
Sun Feb 13, 2011 6:09 pm
Forum: Social Lounge
Topic: Math Books in Ekushey Boi Mela
Replies: 4
Views: 2024

### Re: Math Books in Ekushey Boi Mela

The fair opens at 3 pm
Sun Feb 13, 2011 9:04 am
Topic: BdMO National Secondary (Higher Secondary) 2011/6
Replies: 7
Views: 3175

### Re: BdMO National Secondary (Higher Secondary) 2011/6

Fahim, Well done. Your proof is correct.
Sat Feb 12, 2011 11:45 pm
Topic: BdMO National Secondary (Higher Secondary) 2011/6
Replies: 7
Views: 3175

### Re: BdMO National Secondary (Higher Secondary) 2011/6

Sat Feb 12, 2011 11:41 pm
Topic: BdMO National Higher Secondary 2011/10
Replies: 3
Views: 2077

### Re: BdMO National Higher Secondary 2011/10

This was one of the earliest problems of the question camp (might be even the first one). I like this problem very much, it is a beautiful one. One who solves it should appreciate its elegance as well.
Sat Feb 05, 2011 10:43 pm