mm-629 === Subject: Re: numeric series question by support1.mathforum.org (8.11.6/8.11.6/The Math Forum, $Revision: 1.9 primary) id i9EMtTJ20288; Start with a geometric sequence with the 1st term 1 and quotient -x^k: 1/(1 + x^k) = 1 - x^k + x^2k - x^3k +- ... For k = 3: 1/(1 + x^3) = 1 - x^3 + x^6 - x^9 +- ... The radius of convergence is 1. Inside of the radius, we can integrate term by term. The radius of convergence does not change in the process. At the radius of convergence, the series diverges of converges relatively. For a series Sum (-1)^n*|a_n| with alternating signs, |a_n| -> 0 for n -> inf is sufficient for convergence. S dx/(1 + x^3) = x - x^4/4 + x^7/7 - x^10/10 +- ... S dx/(1 + x^3) = 1/3*S dx/(x + 1) - 1/3*S (x - 2)/(x^2 - x + 1)dx = = 1/3*ln(x + 1) - 1/6*S (2x - 1)/(x^2 - x + 1) + + 1/2 S dx/(x^2 - x + 1) = = 1/3*ln(x + 1) - 1/6*ln(x^2 - x + 1) + 1/2*S dx/[(x-1/2)^2 + 3/4] = = 1/3*ln(x + 1) - 1/6*ln(x^2 - x + 1) + + 1/2*sqrt(3)/2 * S dt/(t^2 + 1) (where t = 2/sqrt(3)(x - 1/2)) = = 1/3*ln(x + 1) - 1/6*ln(x^2 - x + 1) + + sqrt(3)/3 * atan(2/sqrt(3)*(x - 1/2) + C F(x) = 1/3*ln(x + 1) - 1/6*ln(x^2 - x + 1) + + sqrt(3)/3 * atan[(2x - 1)*sqrt(3)/3] + C Since F(0) = sqrt(3)/3*atan(-sqrt(3)/3) + C = 0, C = sqrt(3)/3*atan(sqrt(3)/3) = sqrt(3)/3 * pi/6 F(1) = 1/3*ln(2) - 1/6*ln(1) + 2*sqrt(3)/3 * atan(sqrt(3)/3) = = 1/3*ln(2) - 0 + 2*sqrt(3)/3 * pi/6 = (approximately) = 0.69314718/3 + 3.14159265 * 1.73205081/9 = = 0.23104906 + 0.60459979 = 0.83564885 Generally, x^k + 1 has one real root -1 for odd k. The remaining quadratic factors are: [x - e^(i*2pi/k)]*[x - e^(-i*2pi/k)] = x^2 - 2*cos(2pi/k)*x + 1 and this allows to expand x^k + 1 into fractions, the integrals of which are easy to calculate. === Subject: Re: numeric series question by support1.mathforum.org (8.11.6/8.11.6/The Math Forum, $Revision: 1.9 primary) id i9F28pi03332; >... >Generally, x^k + 1 has one real root -1 for odd k. The remaining >quadratic factors are: >[x - e^(i*2pi/k)]*[x - e^(-i*2pi/k)] = x^2 - 2*cos(2pi/k)*x + 1 >and this allows to expand x^k + 1 into fractions, the integrals of >which are easy to calculate. Sorry for the error. x^k + 1 has one real root -1 for k odd (leading to the ln(2) term in the series sum). The remaining quadratic factors are: [x + e^(i*2pi*m/k)]*[x + e^(-i*2pi*m/k)] = x^2 + 2*cos(2pi*m/k)*x + 1 m = 1, 2, 3, ..., (k - 1)/2 x^k does not have a real root for k even. All the quadratic factors are: [x + e^(i*2pi*(m - 1/2)/k]*[x + e^(-i*2pi*(m - 1/2)/k] = = x^2 + 2*cos(2pi*(m - 1/2)/k)*x + 1 m = 1, 2, 3, ..., k/2 and this allows to expand 1/(x^k + 1) into fractions, the integrals of which are easy to calculate. === Subject: Re: Descrete Math help with question by support1.mathforum.org (8.11.6/8.11.6/The Math Forum, $Revision: 1.9 primary) id i9EMtTB20297; >I'v been trying to figure out this question and i don't even know >where to begin. >Define two Sets A and B as follows: A = {(2n+1)^3|n E Z} and >B = {(2n+1)|n E Z} >a) prove that A is a proper subset of B. >b) suppose we redifine A and B, replacing Z by R . What is the >relation between these two sets? State and prove your answer. You should probably talk with your instructor or your TA if you have no idea where to begin. But: (a) To say A is a subset of B means, by definition, that any element of A is an element of B. Now look at B: it's just the set of odd integers. A is the set of cubes of odd integers. So the statement is that the cube of any odd integer is an odd integer, which of course makes sense. To *prove* it, let (2n + 1)^3 be any element of A, and write it out so that it has the form 2m + 1 of an element of B (please note that the m need not be the same as n): (2n + 1)^3 = 8n^3 + 12n^2 + 6n + 1 = 2m + 1 where m = ? (you do this part). Now: to say A is a *proper* subset means that also not every element of B belongs to A. Here it means that not every odd integer is the cube of an odd integer. To prove this, all you have to do is give an example of an odd integer which isn't a cube or third power of an integer. I'll let you do this. (b) OK, now replace Z by R (the set of real numbers) and try to understand what B is. Using different letters may help: it's the set of all real numbers which are of the form 2x + 1, where x is real. But any real number is of that form: if y is any real, there's an x such that y = 2x + 1 -- namely, x = (1/2)(y - 1). So B is just the set of all real numbers. By the same token, A is the set of all numbers of the form x^3 where x is real. But any real number is of that form: if y is any real, there's an x such that y = x^3 -- namely, what? So A is the set of all reals and B is the set of all reals. Now you should be able to answer questions like: is A a subset of B? Is A a proper subset of B? I don't know if you are required to give proofs in your course, but if you are, you should get in the habit of working straight from definitions. Good luck with your course. Todd Trimble === Subject: Re: Truth Tables Help > I have a four part question in a tutorial, parts 1 & 2 I don't have any > problem with. Parts 3 & 4 I have no idea what they mean. Can someone explain > to me what parts 3 & 4 mean and how can I answer the questions. > Alternatively if you can point me to a website that might be of some help. > The question: > Draw the truth tables for each of the following expressions: > 1. AB'CD' + ABC'D' + A'BC'D + A'B'CD > 2. (A + B' + C' + D)(A' + B + C + D') > 3. Sm(2.5.6.9) > 4. ?M(0,7,10,11) > Appreciate any help. > TIA Whenever I note that the use of language skill in engineering is a valuable asset, I get put down. Here is an example of a problem that is poorly posed and communicated. I have no idea what anything after the colon signifies. I can only guess that earlier in the tutorial there was a discussion of symbology to be used in the remainder of the tutorial. Without knowing what that is, I have no idea on how to help. Bill === Subject: Re: Truth Tables Help Problem with is parts 3 & 3. Parts 1 & 2 read 1. (A and not B and C and not D) or (A and B and not C and not D) or ( not A and B and not C and D) or (not A and not B and C and D) 2. (A or not B or not C or D)(not A or B or C or not D) > I have a four part question in a tutorial, parts 1 & 2 I don't have any > problem with. Parts 3 & 4 I have no idea what they mean. Can someone explain > to me what parts 3 & 4 mean and how can I answer the questions. > Alternatively if you can point me to a website that might be of some help. > The question: > Draw the truth tables for each of the following expressions: > 1. AB'CD' + ABC'D' + A'BC'D + A'B'CD > 2. (A + B' + C' + D)(A' + B + C + D') > 3. Sm(2.5.6.9) > 4. ?M(0,7,10,11) > Appreciate any help. > TIA > Whenever I note that the use of language skill in engineering is a valuable > asset, I get put down. Here is an example of a problem that is poorly posed > and communicated. I have no idea what anything after the colon signifies. > I can only guess that earlier in the tutorial there was a discussion of > symbology to be used in the remainder of the tutorial. Without knowing what > that is, I have no idea on how to help. > Bill === Subject: Re: Truth Tables Help > Problem with is parts 3 & 4. Exactly, so what, according to your text or notes, do Sigma(2.5.6.9) and Pi(0,7,10,11) mean? === Subject: Re: Truth Tables Help First line should have read 3& 4 > Problem with is parts 3 & 3. > Parts 1 & 2 read > 1. (A and not B and C and not D) or (A and B and not C and not D) or ( not A > and B and not C and D) or (not A and not B and C and D) > 2. (A or not B or not C or D)(not A or B or C or not D) at > I have a four part question in a tutorial, parts 1 & 2 I don't have any > problem with. Parts 3 & 4 I have no idea what they mean. Can someone > explain > to me what parts 3 & 4 mean and how can I answer the questions. > Alternatively if you can point me to a website that might be of some > help. > The question: > Draw the truth tables for each of the following expressions: > 1. AB'CD' + ABC'D' + A'BC'D + A'B'CD > 2. (A + B' + C' + D)(A' + B + C + D') > 3. Sm(2.5.6.9) > 4. ?M(0,7,10,11) > Appreciate any help. > TIA > > > Whenever I note that the use of language skill in engineering is a > valuable > asset, I get put down. Here is an example of a problem that is poorly > posed > and communicated. I have no idea what anything after the colon signifies. > I can only guess that earlier in the tutorial there was a discussion of > symbology to be used in the remainder of the tutorial. Without knowing > what > that is, I have no idea on how to help. > Bill === Subject: Re: Truth Tables Help X-RFC2646: Original If I recall correctly Sigma is usually successive addition and the big PI is usually a successive multiplication. > My earlier post should read: > I have a four part question in a tutorial, parts 1 & 2 I don't have any > problem with. Parts 3 & 4 I have no idea what they mean. Can someone > explain > to me what parts 3 & 4 mean and how can I answer the questions. > Alternatively if you can point me to a website that might be of some > help. > The question: > Draw the truth tables for each of the following expressions: > 1. AB'CD' + ABC'D' + A'BC'D + A'B'CD > 2. (A + B' + C' + D)(A' + B + C + D') > 3. Sigma m(2.5.6.9) > 4. Pi M(0,7,10,11) > 3 & 4 should read: > _ > > /_ m (2.5.6.9) > __ > I I M (0,7,10,11) > What do your texts or lecture notes say these notations mean? Guess: > Sigma indicates + over some set, and Pi indicates . over some set--but > what sets? === Subject: Re: Truth Tables Help > If I recall correctly Sigma is usually successive addition and the big PI is > usually a successive multiplication. Yes, but addition of what in this case, and multiplication of what in this case? > > My earlier post should read: > I have a four part question in a tutorial, parts 1 & 2 I don't have any > problem with. Parts 3 & 4 I have no idea what they mean. Can someone > explain > to me what parts 3 & 4 mean and how can I answer the questions. > Alternatively if you can point me to a website that might be of some > help. > The question: > Draw the truth tables for each of the following expressions: > 1. AB'CD' + ABC'D' + A'BC'D + A'B'CD > 2. (A + B' + C' + D)(A' + B + C + D') > 3. Sigma m(2.5.6.9) > 4. Pi M(0,7,10,11) > > 3 & 4 should read: > _ > > /_ m (2.5.6.9) > > __ > I I M (0,7,10,11) > What do your texts or lecture notes say these notations mean? Guess: > Sigma indicates + over some set, and Pi indicates . over some set--but > what sets? === Subject: Probability Theory -- Serious help needed!! Can someone please help me with this problem: The average density of a forest is 16 trees on every 100 square yards. The tree trunks can be considered as cylinders of a diameter of 0.2 yards. We are standing inside the forest, 120 yards from its edge. If we shoot a gun bullet out of the forest without aiming, what is the probability that it will hit a tree trunk? (Ignore the marginal fact that centers of the tree trunks can not be closer than 0.2 yards to each other.) === Subject: Re: Probability Theory -- Serious help needed!! X-RFC2646: Original First , even not aiming, assume that ur shooting in a horizontal direction and at a height less than the height of all cylinders ( trees ), and fix that height. Second, assume that the bullet is a circle of diameter c. Third, assume that the forest is a cylinder of radius 120 yards and ur shooting from the middle of that circle. Now you can imagine that there is a horizontal circle and the bullet will pass from the center of that circle to the edge of it, so whats the probability that the bullet does not hit the edge (hit a tree trunk). it is easier for you to find the probability that the bullet does hit the edge, say it is p, then (1 - p) is the probability ur looking for (hitting a tree trunk). now lets solve for the probability that the bullet does hit the edge. ? (a) the bullet does hit the edge, that means that there is a line of width c which has nothing in it, ( no trees intersect that line ). (b) Ignoring the marginal fact that centers of the tree trunks can not be closer than 0.2 yards to each other, ***Consider the following examples: 1) Suppose there are two slots, say A and B, and there are three different balls, say a , b, and c; and we want to drop the balls in those two slots with no aiming, Then one possible outcome is that we have the three balls in slot A, and nothing in slot B, or another outcome is that we have ball a in A, and balls b and c are in B. There will be 8 different outcomes, this is done by taking (2^3) where 2 is the number of slots and 3 is the number of different balls. All these 8 outcomes are equally probable and thats a major idea you have to understand, so probabilty of having a in slot A is 1/8, and probabilty of having a and b and c in A is also 1/8; Then the number of different outcomes is (V^N), u can think of this as V is the number of slots and N is the number of balls, here we are assuming that Remember that number of outcomes does not depend on the shape of V. a volume V, and we want to compute the probability that there are no different number of outcomes in ((V-v)^N), v in V is ((V-v)^N)/(V^N), thats a major idea you have to understand too.*** average 16 trees in 100 square yards, then in the forest u have an average of Pi * (120 ^ 2) * 0.16, set it equal to N ( number of trees in the forest). Total accessible Area for the trees is : Pi (120 - 0.1)^2, set it equal to S. Surface of a line of width c and length 120 is 120c. ok, now you all information to solve the problem, the probability that we have N trees in (S - 120c) is ((S - 120c)^N)/(S^N), > Can someone please help me with this problem: > The average density of a forest is 16 trees on every 100 square yards. > The tree trunks can be considered as cylinders of a diameter of 0.2 > yards. We are standing inside the forest, 120 yards from its edge. > If we shoot a gun bullet out of the forest without aiming, what is the > probability that it will hit a tree trunk? (Ignore the marginal fact > that centers of the tree trunks can not be closer than 0.2 yards to > each other.) === Subject: Re: Probability Theory -- Serious help needed!! > Can someone please help me with this problem: > The average density of a forest is 16 trees on every 100 square yards. > The tree trunks can be considered as cylinders of a diameter of 0.2 > yards. We are standing inside the forest, 120 yards from its edge. > If we shoot a gun bullet out of the forest without aiming, what is the > probability that it will hit a tree trunk? (Ignore the marginal fact > that centers of the tree trunks can not be closer than 0.2 yards to > each other.) Probability and statistics aren't my forte, but since no one's said anything, I'll take a stab at getting you started. If I'm not mistaken, this is a problem in using the Poisson distribution. The bullet will hit a tree if the centre of the tree is within 0.2 yards of the bullet's line of ßight. Thus, the bullet will make it to the edge of the forest if no tree centre is within 0.2 yards of that line, i.e., if a strip 120 yards long and 0.4 yards wide contains no tree centre. That strip has an area of 48 sq. yds. The mean density of tree centres is 0.16 per sq. yd., or 7.68 centres per 48 sq. yds., and from here it should be pretty straightforward. Brian === Subject: Re: Uniform Convergence > Is there any easy way to show that the function: > f(c,h) = (c^h - 1)/h > is uniformly convergent as h tends to 0? > I am trying to develop logarithms in a different way from the > classical way of considering the integral of 1/x. So I differentiate > c^x with respect to x, and get the limit as h tends to 0 of f(c,h) > multiplied by c^x. Then I just need to define ln(c) as that limit, and > then I need to show it is continuous. The reason why I need to do > that, is that I can then explicitly calculate ln(c)-1 at 2 and 3, show > that one of them is negative and one positive, so there must be a > number e between 2 and 3 for which ln(e)-1=0 (since ln is continuous), > and then go from there. > However to show it is continuous I need to show two things: a) that > the individual functions are cts (this is easy because they are > clearly differentiable), and b) that the sequence of functions > converges uniformly, and this is what I am struggling with. > Any help would be appreciated. > Adam. OK, let's assume that for c > 0, c^x has been defined for all real x, that the usual power properties hold, and that for fixed p in R the map x -> x^p is differentiable on (0,oo), with derivative = p*x^(p-1). Now you want to consider f(c,h) = (c^h - 1)/h to get at the derivative of x -> c^x without use of ln(x). Unfortunately the simplest and most natural route to this involves the integral of 1/x. However, you don't need to define ln(x)! Here's what I mean: We simply note that (*) (c^h - 1)/h = int[1,c] x^(h-1) dx. And as h -> 0, x^(h-1) -> 1/x uniformly on [1,c] (here taking c > 1). Therefore (*) -> int[1,c] 1/x dx as h -> 0. And we haven't mentioned a log yet. As the last integral is a continuous function of c, we're done. Does this do you any good? === Subject: Re: Uniform Convergence > Define c^x in the standard way as follows: > Suppose x is a natural number, then c^x is defined inductively as c^1 > = c and c^(x+1)=c*c^x (the proof that this is well defined follows > from the principle of induction trivially). > Suppose x is an integer. If x is 0, c^x is 1. If x is negative, c^x is > 1/c^(-x). > Suppose x is rational. Then x = p/q, p and q integers and q non-zero. > Then c^x is the solution y of the equation y^q = c^p. > Suppose x is real. Then there is a sequence of rationals x_n tending > to x. So c^x is the limit as n tends to infinite of c^(x_n). > Suppose x is complex. Then c^x is exp(x*ln(c)). > The function c^x is clearly differentiable WITH RESPECT TO c, which is > what we want in the continuity proof, because we simply form the > newton quotient and use the binomial theorem. I'm not sure how you're getting the differentiablity. You'll have things like [(Pi+h)^sqrt(2) - Pi^sqrt(2)]/h. So which binomial theorem did you have in mind? (I know how to show, pretty simply, that if r is rational and x -> x^r is differentiable on (0,oo) with the usual formula holding, then so is x^r for r irrational, but it's a different idea.) === Subject: Re: Uniform Convergence > Suppose x is real. Then there is a sequence of rationals > x_n tending to x. So c^x is the limit as n tends to > infinite of c^(x_n). >To make this rigorous you have to prove that the limit >exists and is independent of the particular sequence >chosen. You also have to show that this is consistent with >the earlier parts of the definition. > [...] > In terms of your earlier points - I had thought of most of these, but > what do you mean for real numbers where you say you need to prove that > the limit exists? > You have to prove that if converges to x, > then actually converges. This is not > trivial. > [...] It's pretty elementary isn't it? Assuming c^r has been defined for rational r, and that the usual power properties have been proven (c^(r+s) = c^r*c^s, ...), I don't see any problem. One thing you need is that c^(1/n) -> 1 as n -> oo, but this is easy. === Subject: Re: Uniform Convergence in alt.math.undergrad: > Suppose x is real. Then there is a sequence of rationals > x_n tending to x. So c^x is the limit as n tends to > infinite of c^(x_n). >To make this rigorous you have to prove that the limit >exists and is independent of the particular sequence >chosen. You also have to show that this is consistent with >the earlier parts of the definition. > [...] > In terms of your earlier points - I had thought of most of these, but > what do you mean for real numbers where you say you need to prove that > the limit exists? > You have to prove that if converges to x, > then actually converges. This is not > trivial. > [...] > It's pretty elementary isn't it? Assuming c^r has been defined for rational > r, and that the usual power properties have been proven (c^(r+s) = c^r*c^s, > ...), I don't see any problem. One thing you need is that c^(1/n) -> 1 as n > -> oo, but this is easy. Depends on how much you're assuming about R. If you get to assume completeness (in the form of convergence of Cauchy sequences), I suppose that it's not bad, but I don't think that it qualifies as trivial: there's a fair bit of grunt work. Brian === Subject: Re: Shawn's Limit >Really? What if f(x) = e^x + 1? > If O(x) is defined as my mystery function, then > It evaluates to -1/(e^x+1) which by the way ramps straight down to 0. > O(9)=.0001 > O(20)= -.00000000206 > so probably a better way to say it is lim(x-->infinity)O(x) = 0 > good for just about everything other than tan(x) or derivations > thereof. > A bunch of things are identically, and sometimes trivially = 0, others > get there really fast. > so..O(x)=0+ What if f(x) = e^(-x) + 1. Then O(x) -> 1 as x -> oo. === Subject: Re: Phrase Structure > Construct phrase-structure grammars to generate the following set > {0^n1^2n | n >= 0} > (I assume that this should be {0^n 1^(2n) : n >= 0}.) This > is really extremely straightforward; you should be able to > do it yourself. Here are a few hints, though. You can do > it with a single non-terminal symbol; the main production > should generate one new 0 and two new 1's. Have you seen a > grammar that generates {0^n 1^n : n >= 0}? If so, just > modify it slightly. Oh, a phrase-structure grammar is a regular grammar? === Subject: Re: Phrase Structure [...] > Oh, a phrase-structure grammar is a regular grammar? Every regular grammar is a phrase-structure grammar, but not conversely. The language in question isn't regular, so a regular grammar won't be possible; it is context-free, though. Brian === Subject: Re: factoring without a calculator by support1.mathforum.org (8.11.6/8.11.6/The Math Forum, $Revision: 1.9 primary) id i9FFbwL05552; >I forget how to facor w/o a calculator, and my math 113 book does not >explain how to factor. If somebody could show me how to factor >x^2 + x + 1 > 0 without using the quadratic formula i would be very >appreciative. You can say: x^2 + x + 1 = 0 (x + 1/2)^2 - 1/4 + 1 = 0 (x + 1/2)^2 = -3/4 x + 1/2 = +/- sqrt(-3/4) x = [sqrt(-3/4) - 1/2] or [-sqrt(-3/4) - 1/2] and so these two values, when put into the equation, give x^2 + x + 1 = 0 which means when these values are taken from x, the result is zero: so the factorisation is: (x + sqrt(-3/4)+1/2)(x - sqrt(-3/4)+1/2) I think. === Subject: Better late than never by support1.mathforum.org (8.11.6/8.11.6/The Math Forum, $Revision: 1.9 primary) id i9FKGNs00622; >I forget how to facor w/o a calculator, and my math 113 book does not >explain how to factor. If somebody could show me how to factor >x^2 + x + 1 > 0 without using the quadratic formula i would be very >appreciative. >You can say: >x^2 + x + 1 = 0 >(x + 1/2)^2 - 1/4 + 1 = 0 >(x + 1/2)^2 = -3/4 >x + 1/2 = +/- sqrt(-3/4) >x = [sqrt(-3/4) - 1/2] or [-sqrt(-3/4) - 1/2] >and so these two values, when put into the equation, give x^2 + x + 1 >= 0 >which means when these values are taken from x, the result is zero: >so the factorisation is: >(x + sqrt(-3/4)+1/2)(x - sqrt(-3/4)+1/2) >I think. michael, Although your post came almost two years after the OP, I was heartened by it. Hopefully dangerman and G.E. Ivey are long gone from this forum. Unfortunately, the likes of them are far too common in this forum. I am glad to see someone who is willing to offer constructive help rather than denigrating comments. Keep up the good works. - MO