Fall 2014 Math 235 Topics and Homework from Bretscher's Linear Algebra. We'll discuss some in Tuesday class - !ed problems are challenges for you to think about - these assignments are always subject to change as necessary. Unless notified otherwise, the Bretscher problems will NOT be collected. [Problem numbers are from 4e - numbers for 3e/5e indicated where possible. Try the problems by the date indicated, and please complete them by the next Tuesday.] ************************************************************************** ************************************************************************** Common course guidelines and links to practice exam problems are on my webpage: http://www.gang.umass.edu/~kusner/class/classes.html Please also see Prof. Markman's old webpage for useful links to other suggested homework and practice exam problems: http://www.math.umass.edu/~markman/math235_spring14_html/math235.html Many of his suggested problems are different from mine, but try them too! ************************************************************************** ************************************************************************** There are also WeBWorK problems for you to do online: https://webwork2.math.umass.edu/webwork2/F14_MATH_235_3/ regardless of your section number. [Recall that your Username is the stuff BEFORE "@student.umass.edu" and your (initial - change it!) Password is your UMass student ID number.] ************************************************************************** ************************************************************************** Supplemental Instruction sessions for Math 235 may take place in W. E. B. DuBois Library 1349 and there should also be tutors available there from time to time. (Please check directly with the SI folks there for details.) ========================================================================= ========================================================================= CAUTION: This page is under reconstruction - please excuse the potholes!! ========================================================================= ========================================================================= *** MINI-MIDTERM EXAM *** ****** 7-9PM Tuesday 7 October 2014 ****** ************* Thompson 104 ************* *** MINI-MIDTERM MAKE-UP *** ****** 8-10 PM Monday 6 October 2014 ****** ************* LGRC A301 ************** [You may use an 8.5" x 11" sheet of notes in your handwriting] [No calculators, etc.] ========================================================================= ***** MAKE-UP MIDTERM (sorry: no review) with Prof. Rob Kusner ***** ******* Monday 3 November 2014 from 7-9pm ******* ************* LGRC A301 ************** *** COMMON MIDTERM EXAM *** ******* Tuesday 4 November 2014 from 7-9pm ******* ********** 131 Marcus *********** [You may use an 8.5" x 11" sheet of notes in your handwriting] [No calculators, etc.] [Make-up conflict? You MUST contact profkusner@gmail.com before 1 Nov!] ************************************************************************** ************************************************************************** *** FINAL EXAM *** ***** 10:30AM Wednesday 10 December 2014 in Totman Gym ***** ***REVIEW & PRACTICE PROBLEMS*** [See my classes.html page for more details, please] ************************************************************************** ************************************************************************** OLD PRACTICE MIDTERM: http://www.gang.umass.edu/~kusner/class/235f11pracmid.pdf ANSWERS: http://www.math.umass.edu/~norman/235_f11/exam/pracmidans1.pdf [and then replace 1 with 2 or 3 to see answers to others] OLDER PRACTICE FINAL: http://www.math.umass.edu/~norman/235_f10/exam/m235pracfinal.pdf ========================================================================= ========================================================================= MORE SPECIAL INFO: This schedule is still being revised!!!!!! ========================================================================= ========================================================================= [There will be copies of Bretscher ON RESERVE in the MAIN LIBRARY] [Please read indicated sections even if no problems are assigned] 09/02 [The following is a *true* story, from the summer of 2010:] I walked into the post office in my late father's village one summer and was greeted by 3 similarly dressed young ladies of whom I first asked "Are you all sisters?" and then realized one was mom and the other two were her daughters (hey, I'm getting old ;-). So while mom was picking up a package, I tried entertaining the kids with a little magic trick of "guessing" their ages. First I "guessed" mom's age (29, of course ;-), but then I needed a bit of information to "guess" the others. So I asked the bigger daughter if she could ADD her age to her sister's and tell me the answer: The SUM was 10. Then came the hard part: how much older are you than your little sister? She thought for a bit and answered: The DIFFERENCE was 4. Then I explained that meant twice the bigger sister's age was 14, so she must be 7 (Yes! the older one squealed), and her little sister must then be 3 (Yes, the little one shyly smiled). And then the mom (who's attention I'd been cleverly trying to get ;-) exclaimed: That's Linear Algebra! [And I did **NOT** reply "OK, let's work this out in detail with pen and paper" - but *you* guys can and should do that now if it wasn't already clear from class (no need to turn this one in) ;-] Note: the same ideas - in fact, the very same equations! - could be applied to a more serious situation, say, where there was a mixture of two unknown ingredients (like electrons and positrons) but only the sum (total mass) and difference (total charge) could be measured, yet we needed to know how much there was of each ingredient (to prevent the universe from collapsing in minutes ;-). * * * An (infinite) chessboard can be thought of as the integer points in the plane: in other words, a possible chess move is of the form mH + nV where H and V are basic horizontal and vertical moves by a single square, and where m and n are (positive or negative) integers. Analyze the various moves of different chess pieces. For example, a rook (castle) can make a basic H or V move, and thus can move to any position on the board - how about a knight? How few knight moves does it take to make a basic H or V move? Bishops move diagonally, and thus (unlike the other pieces) they always stay on their same color. These moves are of the form mH + nV where m+n is even; alternatively, they are of the form aA + bB where A = H + V and B = -H + V are basic diagonal moves. Explain why these descriptions of bishops' moves are equivalent (see next problem for one way to go about this). * * * The atoms in salt (NaCl) are located at the points of the integer (cubic) lattice in 3-space: lI + mJ + nK where l, m and n are integers, and where I, J and K are translation vectors along the axes. If we place a Na atom at the origin O, we have seen that there are two descriptions for the sites of the Na atoms: (*) lI + mJ + nK where l+m+n is an EVEN integer, (**) aA + bB + cC where a, b, and c are integers, and where A = I + J, B = J + K, C = I + K are diagonal vectors on the faces of the cube. We want to see that these two descriptions of the Na sites (also known as the face-centered cubic, or FCC, lattice) are equivalent. To do this, find a formula F(a, b, c) = (l, m, n) which gives the location in description (*) of a point V = aA+ bB + cC in description (**). Also find an inverse formula G(l, m, n) = (a, b, c) which lets us recover the coefficients in (**) from those in (*). As a warm-up, first work out the values of a, b and c you will need to make I + 2J + 3K, in other words, solve the vector system (***) of 3 equations in the 3 unknowns a, b and c so that (***) aA + bB + cC = I + 2J + 3K * * * This was a problem that the NPR "Car Guys" once posed on-air as a Puzzler (their answer may be posted on line, but it may be too late to hear that over the airwaves - please do it on your own): Cats cost $1, dogs cost $15, and mice cost only $0.25. I want a herd of 100 animals, and I have $100, so being a cat lover, it's tempting to get only cats (and mice ;-). But I also want a dog, and my cat(s) want a mouse to "play" with, so the numbers of dogs, cats and mice are each positive. And no cash can be left over. What's the solution? * * * Also, please read the Preface/TextOutline in Bretscher. 1.1 # 10, 12, 16, 18, 24 * * * What happens if we append the row 10 11 12 to the matrix 1 2 3 4 5 6 7 8 9 from class? Its reduced row echelon form has the same 2 first rows as the original: 1 0 -1 0 1 2 (and the remaining two rows are all 0s). Therefore, the corresponding system of 4 (homogeneous) equations in the three unknowns r, s and t still has the same set of solutions as the original (and not only the trivial solution r=s=t=0). What would have happened if we had appended the row 10 11 c with c anything other than 12? And what happens if we keep appending more and more rows like 13 14 15 and so forth? * * * Here's a fun problem that involves not only linear algebra, but also elementary ideas about divisibility or number theory: Suppose you want to make $5 using exactly 100 common US coins. Easy, you say: just use nickels (5 cents each). But I say, no - we have NO nickels, only pennies (1 cent), dimes (10 cents) and quarters (25 cents) - is it possible to make $5 now with exactly 100 of these coins? Why or why not? [HINT: Row reduce the (augmented) matrix 1 1 1 | 100 1 10 25 | 500 and recall that we want (positive) integer solutions, corresponding to the number P of pennies, D of dimes, and Q of quarters.] 09/09 Challenge problem: How many rrefs of an m by n matrix are there? [Hints: try the square (m=n) case first, then distinguish the cases m>n and m= 1. On the other hand, the intersection of V and W is a subspace of both V and W, so its dimension is at most the min of the dim(V) and dim(W), i.e. d = <2. Thus d = 1 or 2 are the only possibilities. These are realized, by the examples V = span{e1, e2}, W = span{e2,e3,e4} and V = span{e1, e2}, W = span{e1,e2,e3} respectively. Now try the same kind of reasoning for the problem at hand. 56 Again, try a case where n is small to get intuition: for n=2, the example | 0 1 | A = | | | 0 0 | works, with v1 = e1, Av1 = e2. If you now just follow the hint in the book, and apply A^{M-1} to the relation sugested, you'll get the equation A^{m-1}(c0 v) = c0 A^{m-1}(v) = 0 which can only happen if c0 = 0, since we assumed A^{m-1}(v) is NOT zero (this defines "nilpotent of order m" - the first example has order m = 2). What power of A would you apply to the relation to get c1 = 0? 10/14 Fall Break (Columbus Day pre-empts Tuesday class - and there will be NO CLASS THIS Thursday 16 October because we moved the mini-midterm from "in-class" to and evening exam) ***************************************************************************** ***************************************************************************** ***Turn in 2.4#80-81,104 and the symmetry probs on Tue 21 Oct*** ***************************************************************************** ***************************************************************************** !!!!!!!!!! THINGS TO PREVIEW - THINK ABOUT OVER FALL BREAK !!!!!!!!!! For the rest of the semester we plan to cover the following topics: Vector spaces, linear maps and coordinates (Chapter 4) Determinants (6.1, 6.2) Eigenvalues, eigenvectors (chapter 7) Orthogonality: Gram-Schmidt (5.1) and inner product spaces (5.5) For those of you not familiar with differential equations, here's where you can learn a little more: www.math.umass.edu/~kusner/class/diffeqnotes.pdf ("Quick and Dirty Differential Equations" notes by Peter Norman, with just a little help from yours truly ;-) !!!!!!!!!!!!!!!!!!!!!!!!!! FALL BREAK ENDS :-(((!!!!!!!!!!!!!!!!!!!!!!!!!! 10/21 4.1 #4, 8, 14!, 24, 26, 36, 40!, 50, 52, 58! [... but do it early!] 4.2 #2, 4, 6, 17!, 20, 22, 23!, 64, 65!, 78! [I have checked the 3e versus 4e problem numbering through here.... Remember to check http://www.math.umass.edu/~markman/math235_spring14_html/math235.html for other suggested problems.... 10/28 4.3 #2, 4, 5!, 15!, 18, 23!, 29!, 48, 49! 6.1 # 2, 8, 14, 24, 26, 32, 38!, 46!, 52! *********************************************************************** !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! COMMON MIDTERM INFO: ***** MAKE-UP MIDTERM (sorry: no review) with Prof. Rob Kusner ***** ******* Monday 3 November 2014 from 7-9pm ******* ************* LGRC A301 ************** *** COMMON MIDTERM EXAM *** ******* Tuesday 4 November 2014 from 7-9pm ******* ********** 131 Marcus *********** [You may use an 8.5" x 11" sheet of notes in your handwriting] [No calculators, etc.] [Make-up conflict? You MUST contact profkusner@gmail.com before 1 Nov!] ========================================================================== Disclaimer: The 235 midterm again comes later this term, and includes different topics than previous 235 midterms, so old practice midterms may not give the full flavor of the topics on this year's midterm. See my and Prof. Markman's website for some practice midterms! Here's a link to an old practice midterm exam: http://www.gang.umass.edu/~kusner/class/m235_fall08pracexam.pdf Here is a link to an even older practice midterm exam: http://www.math.umass.edu/~kusner/class/old235pracexam.pdf And at the end of this file are answers to T/F questions from each chapter end, which may help you to review concepts for the midterm. !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ********************************************************************** 11/04 6.2 # 2, 8, 12, 14, 16, 17, 18!, 20!, 26!, 30 [For 6.2 # 17, 20,... here are hints (adapted from Markman): Let V be a vector space with basis {v_1, ..., v_n}, [ ]:V -> R^n the coordinates linear map, and S:R^n->V its inverse, given by S(c_1, ... c_n)=c_1v_1+ ... +c_nv_n. Suppose T:V->V is any linear map. We construct the composite linear map from R^n to R^n, taking a vector x to [T(S(x))], i.e., to the coordinate vector in R^n of the vector T(S(x)) in V (thinking of our diagram, go up via S, over via T, and down by [.]). Being linear, the composite map is multiplication by the n by n matrix B, i.e., [T(S(x))]=Bx, for all x in R^n. The matrix B is called the matrix of T in the given basis (section 4.3). Its i-th column, by definition, is b_i=Be_i=[T(S(e_i))]=[T(v_i)]. Thus, the i-th column of B is the coordinate vector of T(v_i). The determinant det(T) is defined to be det(B) (see 6.2.11). Now use the equation b_i=[T(v_i)] and the standard basis {1, x, x^2} of P_2, and the standard basis of R^{2 x 2}....] 6.3 # 1, 2, 3 (translate the triangle first so that one of its vertices is the origin), 4, 7, 11 Extra problem for section 6.3: Let A be a 3 by 3 matrix, with det(A)=7, u, v, w three vectors in R^3, such that the parallelopiped determined by them (i.e., the one with vertices 0, u, v, w, u+v, u+w, v+w, u+v+w) has volume 5 units. Find the volume of the parallelopiped determined by Au, Av, Aw. Carefully justify your answer! 11/11 7.1 # 1-6, 9, 10, 12, 15 (see Definition 2.2.2), 16, 19, 38 Extra problem for section 7.1: Find the matrix of the reflection A of the plane about the line x=y. Find all eigenvalues and eigenvectors of A and a basis of R^2 consisting of eigenvectors of A. Find the matrix of A with respect to the basis you found. 7.2 # 6, 12, 16, 20, 28 Extra problem for section 7.2: www.math.umass.edu/~markman/math235_spring08_html/extra-problem-sec7-3.pdf 11/18 7.3 # 4, 16, 26 7.4 # 2, 12, 14, 40!, 48!, 58! Extra problem for section 7.4: www.math.umass.edu/~markman/math235_fall00_html/extra-problem-diffeq/extra-problem-diffeq.html [None of the instructors, including yours truly, got this far, so the following material will not be on the final exam - some WW problems on these topics will be treated as "extra credit" - and of course the material is worth learning!!!] 11/25 7.5 # 2, 8, 24 No class Thursday - please give thanks for your turkey and cranberries! 12/02 5.1 # 6, 10, 12, 18, 28, 36!,40!, 42! 5.2 # 4, 6, 20!, 32, 34!, 40! In class we will have discussed an inner product on the polynomials in x: is the integral of p(x)q(x) dx from -1 to 1. A basis for the quadratic polynomials is {1, x, x^2}. Use the Gram-Schmidt process to convert this into an orthonormal basis with respect to this inner product. [Section 5.5 touches on this also.] 5.3 # 4, 10, 16!, 18!, 20!, 28, 31!, 34!, 37! Extra problem on projections: http://www.math.umass.edu/~markman/math235_spring11_html/extra-problem-least-squares.pdf 5.5 # 2, 4, 8, 9! REVIEW: ***** 5PM Monday 8 December 2014 in the lowrise (LGRC A310) ***** FINAL EXAM: ***** 10:30AM Wednesday 10 December 2014 in Totman Gym ***** ==================================================================== ==================================================================== (Old) Practice Exam: http://www.gang.umass.edu/~kusner/class/pracexam2.pdf Also, please think about this problem: Suppose we want to compute the exponential of a matrix exp(A) = I + A + A^2/2 + ... + A^k/k! + ... - how does having a basis of eigenvectors for A, along with their corresponing eigenvalues, help us?! Practice final solutions (not sure I like the sound of that): http://www.math.umass.edu/~kusner/prac235finalsols.pdf HAVE A GREAT SUMMER!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ==================================================================== ==================================================================== Answers to T/F questions from the end of each chapter for Bretscher _Linear Algebra, 3E [of course, it is YOUR job to figure out why]. !!!!!!!!!!!!!!!!!! Warning: 4E has changed !!!!!!!!!!!!!!!!!!!!!!!!! ==================================================================== ============================no guarantees=========================== ==================================================================== Chapter 1 1 T 2 F 3 F 4 T 5 T 6 F 7 F 8 F 9 T 10 T 11 F 12 F 13 T 14 T 15 T 16 T 17 T 18 T 19 F 20 F 21 F 22 T 23 F 24 T 25 F 26 T 27 F 28 F 29 F 30 T 31 T 32 T 33 F 34 T 35 F 36 T 37 T 38 T 39 F 40 F 41 T 42 T 43 T 44 F 45 T Chapter 2 1 T 2 F 3 T 4 T 5 F 6 T 7 F 8 F 9 T 10 T 11 F 12 T 13 T 14 T 15 T 16 T 17 F 18 T 19 F 20 T 21 F 22 T 23 F 24 T 25 T 26 T 27 T 28 F 29 F 30 T 31 F 32 F 33 T 34 T 35 T 36 T 37 F 38 T 39 F 40 T 41 T 42 F 43 T 44 F 45 T 46 T 47 F 48 F 49 F 50 F 51 F 52 T 53 T 54 T [over the COMPLEX NUMBERS; what about REAL NUMBERS?] 55 T 56 T Chapter 3 1 F 2 T 3 T 4 F 5 T 6 F 7 T 8 F 9 T 10 F 11 T 12 T 13 F 14 T 15 T 16 F 17 T 18 T 19 T 20 T 21 F 22 F 23 T 24 T 25 T 26 T 27 F 28 F 29 T 30 T 31 T 32 F 33 F 34 T 35 F 36 T 37 T 38 F 39 F [although there is a natural way to realize it as a subspace!] 40 T 41 T 42 F 43 T 44 T 45 T 46 T 47 T 48 F 49 T 50 T 51 F 52 T 53 F [this one is tricky ;] ==================================================================== ============================no guarantees=========================== ====================================================================