Discrete math Definition and 206 Threads

  1. L

    Discrete math venn diagram proof

    Prove for all sets A,B, and C : A complement UNION B complement = (A intercept B) complement help me out here please
  2. O

    Discrete Math: Sets/Functions/Proofs

    I apologize for the title, I really don't know how to describe these problems, so I just listed the categories that they fall under. Anyways... Homework Statement Let f: A->B be a function, where A and B are finite sets and |A| =|B| (they have the same size I believe). Prove that f is...
  3. K

    Are Linear Algebra and Discrete Math Essential for Aspiring Physicists?

    From experienece, are these two courses really important to someone looking to major in physics? I've read the "So you want to be a physicist" guide, but if I work with the book Mathematical Methods in the Physical Sciences, will it be enough to make it through the upper level physics courses...
  4. K

    Is Every Rational Number Always a Ratio of Two Integers?

    Rewrite the following statement formally. Use variables and include both quantifiers \forall and \exists in your answer. Statement: Every rational number can be written as a ratio of some two integers. If I didn't have to use \exists I'd write it as follows \forallrational numbers...
  5. G

    What is a complete set of representatives for an equivalence relation on a set?

    Homework Statement Definition: let R be an equivalence relation on a set X. A subset of X containing exactly one element from each equivalence class is called a complete set of representatives. now define a relation R on RxR by (x,y)R(u,v) <---> x^2 + y^2 = u^2 + v^2. You don't have to...
  6. A

    Discrete Math - Complete set of representatives

    [SOLVED] Discrete Math - Complete set of representatives Homework Statement At what temperature fahrenheit is it equal to celsius? Homework Equations (none) The Attempt at a Solution
  7. S

    Need Help [Discrete math / Algorithms]

    Quick Summary: I'm in a class were we analyze code / find big theta / Oh / etc (Algorithm Design and Analysis). It's based on discrete math, which I'm terrible at. After posting Tired of Discrete Math... I have come to the conclusion that I will be needing some help figuring out a way to pass...
  8. S

    Struggling with Discrete Math? Here's What to Do

    Rant Warning I am a computer science major and math is a major part of our curriculum. A year ago I took my first ever discrete math course, and it honestly fried my brain. Now I'm in a computer science course that uses discrete math to analyze algorithms, and my brain has simply shutdown...
  9. V

    DISCRETE MATH: Binomial Theorem proof (using Corollary 2)

    Homework Statement Show that if n is a positive integer, then 1\,=\,\binom{n}{0}\,<\,\binom{n}{1}\,<\,\cdots\,<\,\binom{n}{\lfloor\frac{n}{2}\rfloor}\,=\,\binom{n}{\lceil\frac{n}{2}\rceil}\,>\,\cdots\,>\binom{n}{n\,-\,1}\,>\,\,\binom{n}{n}\,=\,1 Homework Equations I think this proof involves...
  10. K

    Can a Sequence of Consecutive Positive Integers Not Contain Any Primes?

    Could someone help me with this induction proof. I know its true. given any integer m is greater than or equal to 2, is it possible to find a sequence of m-1 consecutive positive integers none of which is prime? explain any help is greatly appreciated thanks
  11. V

    Prove That At Least 1 Integer Divides Another w/ Discrete Math

    Homework Statement Use mathematical induction to show that given a set of n\,+\,1 positive integers, none exceeding 2\,n, there is at least one integer in this set that divides another integer in the set. Homework Equations Mathematical induction, others, I am not sure The...
  12. V

    Mathematica Prove: Sets Union & Intersection Hypothesis

    DISCRETE MATH: Prove a "simple" hypothesis involving sets. Use mathematical induction Homework Statement Prove that if A_1,\,A_2,\,\dots,\,A_n and B are sets, then...
  13. C

    Finding sets, listing sets (discrete math)

    Homework Statement 2. Let A, B and C be the following sets: A = (x є N | x< 25) B=(x e N | x = 2m for some positive integer m) C = (x є N | x = 3m for some positive integer m) Find each of the following sets. In each case, list all of the elements of the set. i) A – (B u C) ii)A n C...
  14. C

    Discrete Math Help (sad story)

    Homework Statement 1. Let x and y be positive integers and assume that xy is odd. Prove the following statement using the method of proof by contradiction: Both x and y are odd. 2. Let A, B and C be the following sets: A = (x є N | x< 25) B=(x e N | x = 2m for some positive...
  15. M

    Discrete Math Help: Rewrite Statement with Logical Equivalences

    Homework Statement Use the logical equivalences p \rightarrow q \equiv \sim p \vee q and p \leftrightarrow q \equiv (p \rightarrow q) \wedge (q \rightarrow p) to rewrite the statement form: (p \rightarrow (q \rightarrow r)) \leftrightarrow ((p \wedge q) \rightarrow r) Homework Equations...
  16. S

    Discrete Math Help: Proving Injectivity of f & g

    Homework Statement f: B => C and g: A => B 1. If f of g is injective, then f is injective. 2. If f of g is injective, then g is injective.Homework Equations The Attempt at a SolutionI know that 1 is true and 2 is false because I found those as properties, but I am not exactly sure why, and...
  17. V

    DISCRETE MATH: Use rules of inference to show that

    Homework Statement Use rules of inference to show that if \forall\,x\,(P(x)\,\vee\,Q(x)) and \forall\,x\,((\neg\,P(x)\,\wedge\,Q(x))\,\longrightarrow\,R(x)) are true, then \forall\,x\,(\neg\,R(x)\,\longrightarrow\,P(x)) is true. Homework Equations Universal instantiation, Disjunctive...
  18. V

    DISCRETE MATH: Determine whether an argument is correct or not

    Homework Statement Determine whether the argument is correct or incorrect and explain why. A) Everyone enrolled in the university has lived in a dormitory. Mis has never lived in a dormitory. Therefore, Mia is not enrolled in the university. B) A convertible car is fun to drive. Isaac's car...
  19. V

    DISCRETE MATH: Determine if two statements are logically equivalent

    Homework Statement Determine whether \forall\,x\,(P(x)\,\longleftrightarrow\,Q(x)) and \forall\,x\,P(x)\,\longleftrightarrow\,\forall\,x\,Q(x) are logically equivalent. Justify your answer. Homework Equations P\,\longleftrightarrow\,Q is only TRUE when both P and Q are TRUE or...
  20. V

    DISCRETE MATH: Are these system specifications consistent?

    Homework Statement Are these system specifications consistent? "(A)Whenever the system software is being upgraded, users cannot access the file system. (B)If users can access the file system, then they can save new files. (C)If users cannot save new files, then the system software is not...
  21. A

    Understanding C(n,1) in Discrete Math: Solving the Mystery of C(n,1) = 1

    C(n,1) ... I know that C(n,0) =1 But have no clue how to figure out C(n,1) :cry:
  22. B

    Can Set Theory Prove Equality and Intersection Properties?

    Hi, I would like some help for the following problems. please bear with me with my special notation: I- intersection U- union S- universal set ~- complement I need to prove that: let be A and B two sets. prove (A U B) I (A I (~B))=A what I did is: (A U B) I (A I (~B)) =[(A I B)...
  23. B

    Proving the Uniqueness of Solutions for Linear Equations with Real Coefficients

    Hi, Please can someone help me with this problem. show that a,b,c are real numbers and a#0, then there is a unique solution of the equation ax+b=c. the uniqueness of the solution is my problem. Thank you B
  24. E

    Solving Discrete Math Questions - Does Integer Set Include 0?

    I am in discrete math class right now and trying to get the sets of numbers straight. So, does the set of integers include 0? Is it ok to use 0 in proofs, that makes finding a counter-example a lot easier and disprove a statement about all integers. Was just wondering if that is legal...
  25. S

    Can a Pseudograph's Degree Sequence Form an Even Sum?

    Question 1 -------------------------------------------------- "Prove that if (d_1, d_2, ... d_n) is a sequence of natural numbers whos sum is even (n>=1) then there is a pseudograph with n vertcies such that vertex i has degree d_i for all i=1,2,...n" So we have a sequence of natural...
  26. S

    [Discrete Math] Recurrence Relations

    Question: "Find a recurrence relation and initial conditions for the sequence {a sub n} if a sub n is the number of bit strings of length n that contain three consecutive 0's." So here's what I have so far... n > 3 n = 4, 1000, 0001 n = 5, 10000, 00001, 00010, 01000, 10001 n = 6...
  27. S

    [Discrete Math] Permutations / Combinations Advice needed

    One of the class objectives is to give an oral presentation to the professor. This time it has to do with explaining Permutations and Combinations. We have 4 things we need to explain: 1) Permutations / Repetitions are not allowed / Order Matters 2) Combinations / Repetitions are not...
  28. S

    [Discrete Math] Circular Permutations

    "Six men and 6 females are to be seated around a circular table. Every person must be sitting opposite of another person of the same sex. How many different seatings are possible?" * Ok here's my logic, If you have 12 people, and just want to seat them, you can do so in 11! ways... * So...
  29. N

    Finding the Right Book for Self-Studying Discrete Math

    I am planning on self studyint Discrete Math. What would be a good book for this?
  30. N

    Discrete Math Knowledge & Computer Programming

    How useful is the knowledge of discrete math for computer programmers?
  31. N

    Discrete Math and its Usefulness to Electrical Engineers, IC Designers

    How useful is discrete math to an electrical engineer; particularly how useful is it to an ic designer?
  32. S

    [Discrete Math] f: A->B; surjective? find necessary & sufficient condition.

    [Discrete Math] f: A-->B; surjective? find necessary & sufficient condition. Ok in practice for my discrete exam, I have the following problem. Let f : A->B be a function. a) Show that if f is surjective, then whenever g o f = h o f holds for the functions g,h : B -> C, then g =h. b)...
  33. S

    [Discrete Math] Relations, (R subset S) / (R Intersects S)

    [SIZE="1"]Ok; this is another thread that covers two questions. I didn't want to mix them with my previous post; it's from the same 'section' but the questions are different. If any mods have issues with this, please say so. 1) If R \cup S is reflexive, then either R is reflexive or S is...
  34. S

    [Discrete Math] Relations, symmetric and transitive

    Ok so here's one of the questions we've been assigned... So I can graphically see what this relation looks like, and from that I've shown it's reflexive. Now I'm working on proving it as being symmetric, but I can't put it into words. b) ~ is symmetric. Well we want to show that aRb ->...
  35. S

    [Discrete Math] <=> related question.

    Ok so I have two propositions; for ALL x: (P(x) or Q(x)) and I have... (for ALL x: P(x)) or (for ALL x: Q(x)) I need to show if these are logically equivalent. My original assumption was that these are <=>; but that turned out to be wrong. I'm clueless as to what to do... Some hints or...
  36. S

    Discrete Math Proving some power sets

    Ok so I need to prove (by contradiction) that... if the power set(A) is a subset of power set(B), then A is a subset of B. I was given a hint to use proof by contradiction, but in general I'm lost as to what to do... I know the power set of (A) is {B|B subset A} and the powerset of (B) is...
  37. A

    What Is the Smallest Value of k for Postage Using Only 4-Cent and 9-Cent Stamps?

    Hi, This is one of the question from my hw, i don't even understand what it's asking? Please shed some light on it.. thx what is the smallest value of k such that any integer postage greater than k cents can be formed by using only 4-cent and 9-cent stamps? Show that k cents in postage...
  38. S

    Proving (A U B) x (A U B) = (A x A) U (B x B) with Discrete Math

    Hello, How do I proove : (A U B) x (A U B) = (A x A) U (B x B) if and only if : (A C B) or (B C A) ? Please Advice, Dimitry Haritonov
  39. S

    Proving Lattice Property in Dual Posets: A Discrete Math Question

    I have a question from hw, the question is stated "Show that if the poset (S,R) is a lattice then the dual poset (S,R^-1) is also a lattice" I know by Rosen theory that the dual of a Poset is also a poset but how can i prove that it is also a lattice, what def. am i missing. Any help would be...
  40. R

    Solve 2^27841 mod 34 by Hand: Discrete Math Problem Solution

    could someone show me how u would solve 2^27841 mod 34 by hand? I know what theorm to use, I am just having trouble using it? Thanks
  41. R

    Is f(x) = 2x Onto, One-to-One, or a Bijection for Different Domains?

    Hey if anyone could help me with this I would be sooo grateful. I am trying to grasp the idea of onto, one-to-one and bijection(both) functions. A sample problem is: If f(x) = 2x . What is f(Z), all integers. What is f(N), all naturals. What is f(R), all real. These are 3 different problems...
  42. J

    Where Can I Find Resources for Geometry and Discrete Math in Grade 12?

    My life is miserable already first week into grade 12. This stupid book they have given is like Socrates, it asks questions but it only gives ugly pictures and more questions. The examples barely relate to the questions, and our Master Teacher only does examples. Of course I am not a brilliant...
  43. S

    How Many Ways Can You Arrange a Pharmaceutical Board and Solve Math Problems?

    1) The board of directors of a pharmaceutical corporation has 10 members. An upcoming stockholder's meeting is scheduled to approve a new slate of company officers (chosen from the 10 board members). A) 4 (Presendent, Vice Presendent, secretary, and treasurer) positions needs filled. How many...
  44. T

    Why Are These Discrete Math Problems So Challenging?

    I don't know why but these types of problems always seem to kick my butt. Any how here they are and my best guesses as to the correct answer. 1. Danny has 12 different lures in his tackle box that he takes on a five day fishing trip. On each day of the trip he fishes with the same...
  45. T

    What are the connections between Catalan numbers and Pascal's Triangle?

    There are a few areas I wanted to make sure I understand what is going on in with discrete math. I have a test tomorrow over these topics and so this is not exactly homework unless you count studying for a test as homework. In any case I will do my best to explain what I know or don't know and...
  46. B

    Find a: Solve Discrete Math Problem with a & x Intergers

    ok the problem is Given that a and x are intergers, a>1, a|(11x+3), a|(55x+52), find a. I am not sure how to even start this one to find a...any help please :cry:
  47. E

    Prove: |a-b|≤|a|+|b| using Definition of Absolute Value

    Prove that for any vectors a and b, |a-b| is less than or equal to |a| + |b| I'm kind of lost, b/c i can't see a case where |a-b| would actually result in a value being less than |a| + |b|. I've tried doing a proof that is similar, and when I was taught, the definition of absolute value...
  48. S

    Discrete Math Help: Is x Rational?

    Discrete Math Help! Here is the problem: Suppose a, b, and c are integers and x, y, and z are nonzero real numbers that satisfy the following equations: \dfrac{xy}{x+y}=a and \dfrac{xz}{x+z}=b and \dfrac{yz}{y+z}=c . Is x rational? If so, express it as a ratio of two integers...
  49. E

    Discrete Math: Finding Angle Between Plane & XZ Axis

    How do you find the angle between the co-ordinate axis (i.e. the xz plane) and another plane in general?
  50. D

    Geometry and Discrete Math Links

    Would anyone happen to have some links which briefly explain some of the laws in geometry and/or discrete math? At the moment, i am looking for a summary of the Properties of Circles . Thank you for being as helpful as you always are. -- ps I found MathWorld, although i can not find...
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