Return Styles: Pseud0ch, Terminal, Valhalla, NES, Geocities, Blue Moon. Entire thread

Counting Proofs

Name: Anonymous 2006-11-12 16:24

Hay /sci/, having a little trouble with these two proofs ..

1) Let p1, p2, ... p7 be 7 points that are contained in a circle centered at (0,0) with radius 1. Prove or disprove that there are two points p(i),p(j) such that the distance between p(i) and p(j) is strictly less then 1.

Can I just say that a regular septagon with sides of length one cannot be contained within a circle of radius one? If so how would one go about in proving it?

2) Let A = {1,2,3,4,5,6,7,8,9,10,11,12,13,14}. Prove that if I select 9 distinct elements from the set A, that there are at least two pairs of elements whose sum will be exactly 15.

This is obviously true since selecting 9 will give him the majority of the numbers and since the numbers are in a sequence there will always be one number that they can pair with. But like the problem above.. how would one prove this?

Name: FiddleMath 2007-11-30 18:18

Seeing as this dude's homework is long overdue, and that I can get here from Google:

1) Disproof: let p1 through p6 be the points of a regular hexagon, inscribed in the unit circle, and let p7 be (0,0). The distance between every two points is 1 or greater.

2) Anon's answer is largely correct, but it's important to note that the seven pairs of numbers that sum to 15 (1+14, 2+13, ... , 7+8) partition the set {1,...,14}.

Newer Posts
Don't change these.
Name: Email:
Entire Thread Thread List