Some more brain exercises!

1. Jun 20, 2004

1+1=1

hey i have more problems that can really exercise the mind! here are 3.

1. prove if q is divisible by (r +s) then either q is divisible by r or q is divisible by s.

2. if d>0, (fd+ed) = d(f,e). proof.

3. a divisible by b => a^m divisible by b^m a,b,m are in Z+.

i think i have some thoughts and i will share.

1. say that (b+c) = ma, where m is in Z+. after that, i am guessing...

2. could use contradiction here. say that d=0, then show the proof? anyone has any takes on this?

3. there exist m and n s.t. bn=ma. lost after here.

2. Jun 21, 2004

Muzza

For number 3, just apply the definition of "divisibility"... There is a k such that a = bk, and thus a^m = (bk)^m = b^m * k^m, and so a^m / b^m = k^m \in Z, hence b^m | a^m.

3. Jun 21, 2004

matt grime

what does the notation in 1 mean, are you talking about ideals?

the second follows, i believe, if you show the RHS divides the LHS and the LHS divides the RHS

4. Jun 21, 2004

Gokul43201

Staff Emeritus
What does (a+b) denote ?

5. Jun 25, 2004

AlMacD

Number 1: By (r+s), do you mean the sum of r and s? If so, a quick counterexample: 25 is divisible by (2+3) but it's not divisible by 2 or by 3.

6. Jun 25, 2004

Zurtex

Bah, I was just about to put the exact same counter example up