Recent content by math_nerd

  1. M

    Game Theory: Winning Moves for (20, 21, 28)

    (1 pt) We shall denote a position in three-pile Nim by (a,b,c), so that there are a chips in the first pile, b in the second, and c in the third. Given the following position in Nim, list all winning moves. As an example, if the piles are (2,2,2) then we can list all winning moves as...
  2. M

    Programs Math Major at UCSD, and feeling depressed about the future.

    First of all, I used to be the kid that hated math back in high school. But did okay, besides in PreCalc. I go to UCSD now, it's my junior year, and I'm now a Math-Computer Science major. I only declared CSE recently. I got a D in my modern algebra class. I studied super hard too, but didn't...
  3. M

    Proving H = S_4: Lagrange's Theorem

    * H is a subgroup. And how is this true? I'm pretty lost on how to show this.
  4. M

    Proving that H=S_4 for H subset of S_4

    Suppose that H is a subset of S_4, and that H contains (12) and (234). Prove that H=S_4. The order of S_4 is 24. (12)(234) = (1342) shows that the finite subset of group H is closed under the group operation, so it is a subgroup of H. Then, using Lagrange's Theorem, |S_4:H|=24/2 = 12. so...
  5. M

    Converse of Lagrange's Theorem is false

    Hmm...okay. So here's a problem in the book that I think applies this concept. Prove that group order of 12 must have an element of order 2. This problem uses the converse, because 12|1,2,3,4,6,12. But by Lagrange we can say that order of 2 is definitely there. But to prove that order 3 is not a...
  6. M

    Converse of Lagrange's Theorem is false

    This is not a homework problem. In Gallian, there is an example given: The group A_4 of order 12 has no subgroups of order 6. I can't seem to understand what this means in terms of how this is the "converse" of Lagrange's Theorem.
  7. M

    Proving H = S_4: Lagrange's Theorem

    Suppose that H is a subset of S_4, and that H contains (12) and (234). Prove that H=S_4. The order of S_4 is 24. (12)(234) = (1342) shows that the finite subset of group H is closed under the group operation, so it is a subgroup of H. Then, using Lagrange's Theorem, |S_4:H|=24/2 = 12...
  8. M

    Proving that H=S_4 for H subset of S_4

    Suppose that H is a subset of S_4, and that H contains (12) and (234). Prove that H=S_4. The order of S_4 is 24. The order of H is 2. (12)(234) = (1342) shows that the finite subset of group H is closed under the group operation, so it is a subgroup of H. Then, using Lagrange's...
  9. M

    Show mapping is an automorphism

    I want to know if the way I have choose g'=c-di and g=a+bi to be two elements in G is written with the correct logic? For the part I said I did the arithmetic, I did incorrectly. I want to prove the mapping from G to G is onto. So I need to show that phi(a+bi)= c+di. How?
  10. M

    Show mapping is an automorphism

    So I have to show group G maps to itself.
  11. M

    Show mapping is an automorphism

    So I need to show that the mapping Phi(a+bi)=a-bi is an automorphism of the group of complex numbers under addition. The way I have proved it is to show that it is a mapping (we are given this piece of information), the mapping is 1-1 and onto, and the operation is preserved. Also, I assumed...
  12. M

    Show mapping is an automorphism

    So for part 2, I can say that a-bi=c-di, so a=c and b=d must be true for a-bi=c-di. This then implies a+bi=c+di is true. Also, is rest of the proof right?
  13. M

    Show mapping is an automorphism

    Show that the mapping Phi(a+bi)=a-bi is an automorphism of the group of complex numbers under addition. I have this as of now: Let (c+di) and (a+bi) be elements in group G. 1) phi(a+bi) is function phi from G to G, by assumption. Therefore the function is a mapping. 2) 1-1: assume...
  14. M

    Fibonacci sequence: what's wrong here?

    Let me give another example, like to prove that f3n is an even integer, we can apply the formula, and it works. But in the problem stated above, it does not seem to work the same way. It only works when you add F2n+1 to both sides of the equation.
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