21b Final Fall 2002 solutions

Linear Algebra with Applications

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Unformatted text preview: Name: 1 2n Snug/d kg 1 Math 21b Final Exam Tuesday, January 14‘“, 2002 Please circle your section: Tom Judson Andy Engelward Andy Engelward Katherine Visnjic (CA) Jakub Topp (CA) Erin Aylward (CA) MWF 9-10 MWFlO-l] MWF 11-12 — “— _ n“— 12 - 12 :- You have three'hours to take this final exam. Pace yourself by keeping track of how many problems you have left to go and how much time remains. You don't have to answer the problems in any particular order. So move on to another problem if you find you're stuck and that you are spending too much time on one problem. To receive fiJll credit on a problem, you will need to justify your answers carefully - unsubstantiated answers, even if correct, will receive little or no credit (except if the directions for that question K specifically say no justification is necessary, such as the TmefFalse). Please be sure to write neatly - illegible answers will also receive little or no credit. If more Space is needed, use the back of the previous page to continue your work. Be sure to make a note of that so that the grader knows where to find your answers. You are allowed one page of notes on it during the test, but you are not allowed to use any other references or calculators during this test. Good luck! Focus and do we!!! Question 1. (20 points total) True or False (2 points each) No justification is necessary, simply circle T or F for each statement. 6 F (a) If A is a 2 x 2 matrix with det(A) = 0, then one column of A is a multiple of the other. 7;“. — oébt'=c3 Mums nakfifl-J < 1 I ca/umns cum-L Liteng ijcvnv: are (he): '9‘ b] 0111.: a”; ,, 5g 54: .1: qJ-bc=c ow“ aJ =Lc_’ “A :C “neon-4c.) 714n- -&—’— -_-.- 1‘— ’ I-‘I Zn I I air—Q ' Mn L “F 4t .L c. t. c‘ :0) M“) 15% +mo Minivans ILA-'1; “wif‘lrkfi '5 E‘GL- yTKI-r- O)- a F (b) The matrix ATA is symmetric for all matrices A. q IM'l‘I-t‘k '5 SUMMCEF‘I'L "-+ 11w‘f‘5 H: own #‘wlhfi' T_ T as and: art) __pc4/ was; s. :5 (m '“Je-r' ‘CPMIJJ :Am a F (c) If A andB are invertible n x n matrices, then AB and BA are similar matrices. Li’s—5, VJL- low-w- M «J M art'— snzmi-w‘ 7‘F “1% use: «a hawfibca “tax S van SMS‘EM kerb gr- a-“J Bad} 'hlj USinJ S: 8/ at,“ {5 (FE) B" = M as" = M w-..._. mh'iinr- M'i'mkaé T F (d) IfA is an invertible matrix whose eigenvalues are all positive, then the eigenvalues of A2 must be the same as the eigenvalues of A. Mo‘l' +nurv 13-; {flasnuqluu if A} =rL Sn‘nPb TEAL K STHI-I‘C- a; The. tljefiuqiu‘b at A) 4," gr- {fifhmuL if A: ‘ikcn. A's eigenm(u:6 1ft, i 1"} EA] EVT 4*: LL 53] 4-“ wmlm I «J (sf-4V T @ (e) If A is an 2 x 2 matrix with determinant 6, then the determinant of 2A must equal 12. 8Q.- i/ ant. (“out 5‘: A- L & mere—Ans “but. Jgkrm.‘a\=n‘i— b a: cellar" A) 5;», mqu'fl-j't‘fij £01k Fifi-v93 Le. / WES a... lemma (:3 « 413V 03 ‘1‘, s. in (EMT—1‘4 T a) (D If 171 and i"2 are both eigenvectors for an n x n matrix A, then the sum, 17, + 17, , must also be an eigenvector of A. Md" “Well? 1 TC :7: n-‘J \7: H fi-jtnu-LLTIWP‘S HIE-1N “ha: 4—) ‘Hn‘v‘k 3‘5, fi+fil art“ «is: be. (A 55trw'f-Cllbr“ Of’xwvflk no. C*-~c»‘-lel— A: I 3,7cfiflfbfii 5;: E] 5 SM 9‘33"“!- .'3 an noggnu-exj'or- 5 MT— “ e-jand-ar“t fi+fi=ijj r “J ZR] x 5‘ Eh] /‘\ a F (3) HA is anyf'fi‘l " mam the“ detMTA) cannot be negative. Jar (HT/4) -= Ciaf—‘(HTJ alarm), ear M647): 91.1204) 5:. = Qatari-5): "Lela C3 '20 T @ (h) There are invertible 3 x 3 matrices A and S such that SIAS = -A. mi {3055th “'- ol-etbr Mil-~13 / «(Us (wars) = Arcs“) Jet—CA") his) =- figs Lem LrS 24;“), Lur MK—fl)=JLt(-I3)J_gtC4}:—cl¢@ so eta-mfiwtntétj, s. ctr-2+ :6, Ln“ hm ,4 an“? In; twu‘rb'btg. T Gigi) If fil,fiz,...,§m isaneigenbasis for bothA and B, thenA andBmust be similar matrices. Na'i- AER—£154th "" :4: M3 LuJ flue, Saw-vs. mammal-u «viii. rm we, cons-4w [m ~- 1:2 :1 at)“ LuS hgmbalus 1.,e.._ infl— 7113 an; Jet:- ;b m?" sail».th a; S" IL: ll II \ ce on L._._1 T F (j) Suppose 0 is an eigenvalue for two. :3 x n matrices, A and B. Suppose the geometric multiplicity of 0 is the same for both A and B, then A and .3 must also have the same rank. 8 malt—maliu'ij) mwii‘ialic'ii‘ .p O Cir—L?“ Cher-Ml), J -'= “HIM-3,. same i?»- AIR 5'- quUL Lola Iii/R a-HL fink-“NJ hen 3: hank :3"- fl --- nu Question 2 (10 points total) Find the determinants for each of the following matrices (2 points each). Be sure to show all your work, and justify your answers (i.e. just writing down “0,” even if it’s correct, will not be considered a complete answer). 1 2 3 -' 1 You. CAIN ink-3 T‘Lt .Rfiq‘lt- L pm? 0 3 3 -3 , J “A 3 __ x (a) be?!“ ail-43; CJNLLLC r Inca-xv its cf»: mu... {rd—ST l 2 0 .J h 2 0 2 2 *3 Citnflj +Lt. 3’ tin-f ‘1 Ofmmnfi Inn-IL Sum/Jimmq rt J's-r but) dumn‘i) Se =' O i 1 0 U ] .715: ‘IS GIN-«051‘ q- lww +r‘9-mcjuler xvi-Jr'ch ."F (b) 0 —1 3 0 jun it.qu 11.1 is? an H” was) hm 5'qu The M] ed e. I i 1 ‘—I 0 0 l. “Jr 3 NUS \jlu [ah-f a : “Nihk EMIRE" 2 0 0 0 o -1 ‘5 0 e1 Lu‘ +0 ‘6. I. o a I Maw-J mimic. :53“ "MJC— De Dov-i SwaflS, film ‘h-HL JL'RJ‘MIkflfi-I- (J's-inij “{ m-uJ 2‘4...- JdUmQx—st [IS F-6 (or-‘coad .115; {fl MT— “: P‘ A. . _ '$ MAE?! L3“: 11 ' “I153 mix-«‘1’ — (c) The 2 x 2 matrix representing a 210 degree rotation counterc ookwme. lands can}: a,“ M715“ Wan—x : [corn ~55...) sakn L-Slc pLj‘trM-vkfi-u—f— = Lale — (-— 5.3x) -= Loft“! +311'1x: ‘1. (cl) The n x 71 matrix representing a dilation by a factor of 10. go '6"; M‘HIK licks “a; [lawn 1g“ "'4‘ H.“ .1. JJ Er fan so W n ml; (e) The 5 x 5 matrix representing a transformation TUE) that has the effect of swapping the first two standard basis vectors, and that has no effect on the other standard basis vectors, i.e. T(é‘1) = 51, T(§2)=é‘1,andT(é})=§i,fori>2. a. D l O 0 0 ma. -‘ in LCS 3' Ts {w- e O :5 r 0 O U 6 O l 0 O o l H.” o _ when; S'qu it '3 G 0 OD {QM I? I 5.. fires-11¢? = —I Question 3. (6 points total) Find all values for k such that the following homogeneous linear system has nontrivial solutions (i .e. nonzero solutions). 1: + 3y — 22 = 0 2x + y + 33 = 0 5x - 5y + k2 = 0 c; "hos Sjsfem. ‘l‘o luxu— nan-Tmb-‘xl Sah'hing Mn +7~L Mk 0? no mam-Lars mm». mst I“. a L Les: flu" 3 #L qwjmfill mf'r-rg l—n Pro; «rah-d JHJT LIL was 5.2m; x=j=2=0)- S. calm“: ml“: ’2 a :9 ~l r 3 ‘1 1 l 3 —>Lcr) a 0 —§ ‘1 ~(-r) 5' —5- k -* $611) 0 ~20 Jot-Io -‘f(IE) / 3 -l ¢—> [o J -?’r] We‘re mil" r; A no? 0 0 k4? Del-l; Jam-T T)": tale-w- huff—— 71; our 1w... mac c 3 Pot-J i0 0 E—r‘a’] Is, [a o 0]) slut. fr 1c Ls Luis a, rmlc (3/ 0M:S-¢~ LVle #0/ flak“ I‘m-C: "L32 134’. Sat-x L:-. is 'h—‘L +P:;:wl i=3 = ' (Duel-{J MALI-n. fiat 147‘ .g 6 it W113 Question 4. (10 points total) (a) ('7 points) Find a basis for the orthogonal complement of the subspace of R4 spanned by vectors 1 —4 -3 _3 , 6 , and 7 . —4 —2 6 3 3 —4 .L ._- l "7' '3 ‘ SD ; A '— -3 6 mm Ht'm Isak-IL] ‘Rr .37 :51 .1: ‘11: J‘JE’T— flaw-Ll "t.- T.l"3"‘1‘3 [—3—‘13 [an-f 6 —:L 3]+‘1CI) -—> [o -G 4'? 15'1-3-0‘) o a -e. 1' _§(:[) ( > (—3 -v 3 +3017] a o {-14, x,=~5‘5+?{13 o O o o o X3=Sl {1:15 -F i/, £6 : 5 _3 +t 57.1 J S. A Last}, “9 an. I O .. o l orbxojami Cue-’LIOWT- l; Dwtn *5” c, -3 so I J O O .1 (b) (3 points) Suppose that A is a symmetric 6 x 6 matrix such that the image of A is equal to a 2- dimensional plane in R6. Is it possible to determine whether or not 0 is an eigenvalue for A? If so, is it also possible to determine both the algebraic and geometric multiplicities of 0'? If it is possible, then find these, if it is not possible, then explain why not. 5. 1.; mum): A =rc~~k0¢L I, “(A Howe, < j 1‘) flail“: / {Amr (4‘ :5 JJMMJh—L, Ii? in; am. tajeab-usil; (mag «a «(7:1)me NJ Wad-n; MHlfipl.;.7l;¢ «0-4.... Wu, 5. 911'. MsKfiPlfoiv .19 75a; 0 eigenvalue: din} Gear-(figu=‘/== «lfiebr-u—e Mugfipfiufj A: Q; 6:"; jes a I": an eafimwiw— 1GP Question 5. (12 points total) (a) (4 points) Let 1’“ be the linear space of polynomials of degree n or less. Let T : P3 —> R1 be defined by T(p(x)) = xap"(x) , where p(x) is a polynomial in P3. Show that Tis a linear transformation. CLficjc: I; 7—(PCX)+7JX)J Z 7—(Pfixy-Lfll—(TCAU) fir {57,6 ' TKP‘WTW: “3 000%“) if : XVPW WW) = x3 PHCKJ + {2 crflcid : {Var is 711:9sz = I: Tdfmj ‘Rr all he It?) We {)2 ? me.” 771‘ (900) : K3(kP(X))//=~ {3 k ‘9'le = 12641315?!” = RTGWU w” 5., 31.: 773,100): >89"sz is a 1.1m edema.” (b) (2 points) Find a basis for the kernel of transformation Tand determine its dimension. Pix.) '3 jen‘i' is 0 L3 TQM) = o f ml “5 “air: p”dx)=oj. the. M5 :4“ Pal=a><+b (4:,— 11;th Mamet; P’Yxiio/ :- npfll);0-J 71...; a L—srs (.1, a... we a? ‘7‘ r; 55% L4 {‘«XL an JAE-g2“ .3 ; Question 5 continued. . . . . . 1 (c) (6 pomts) Conmder the hnear space V consisting of all 2 x 2 matnces for which the vector|: I] is an eigenvector. Find a basis for this space and determine its dimension. L” ’4: Z: iL :1 1/} am A 1—1!) : 2:; gr :we. v.1“; kt Question 6. (12 points total) 2 l I D l 1 (a) (6 points) The matrix A = 1 2 1 has eigenvectors 1 , 0 and l . Find an orthogonal 1 l 2 — 1 — l 1 matrix S, and a diagonal matrix D, so that A = SDS" CJxLIL-k 'Hu’. fit‘jmdafuaé B? 'h-v. 3 bkjenu—LCHWS ,' II | A, : Q‘vfilo‘g—= 1) A Z {0] )- C-UHLAI. 3-" I 43‘”. _l ___] “I -|| “J A’[::) =3 e-UAL‘L '5 L/ . Si 1L0 an orkcjgflq( l' MIL-h“ six 3) w; c-I'q‘ 7— )“fl— c. M +14% V‘CLT‘OF'S/ we. MLJ +0 orMMMII-a (m cm.» Sdmflt) 3hr, Muck} J-wwLuLf' MT The. 3"] Emir—+134- I: oft—r.ij -L “h: M ‘C-‘hff‘ {—W' (“mm mm Jfl‘emt emu.“ Qr- « gamma. mm: Sir-IL. 4“...)qu WJ-Lwixr +0 Buck Omar) §~ we. n-uJ +1. G—S 1‘1”; HT“ #1.: 6 wafers: I : a O [I : i— -h. QM U: the o .. [o] .[Vfi ) VJ; I d: “I / 2' hi ‘I -l/Ji -yJ—i /ra ~ ‘5 27f; V:- 50 OM LL Nib L I S S j J yr: "/52 V3} J/J'i "I/JZ :45 Question 6 continued. 3 12 — 4 — 6 equal to 2. By diagonalizing B calculate 3'0 (note 2‘“ = 1,024) [mg bbcnmru-LS' O "J A (‘pwm Jlf=Qj Y-lx _5m 6] wt 9 m (b) (6 points) Consider the matrix B = [ Note that B has determinant equal to 0 and trace So 13 el‘jtnfldori : t EILku (AIL—B) :5; so Ma. S: [:31] a.“ veg}?! (.J 9%: ;, gzsass-g an; gummy = r: a [Z :q [2: :1 Question 7. (6 points total) Suppose that if, , 1'52 , . . . , it are eigenvectors of an n x :1 matrix A. Let Vbe the subspace spanned by 171,115”... , i2} . Show that if if is a vector in V, them-ii is in Vas well. (Note, Fl, 17}, . . . , it isn’t necessarily an eigenbasis, as I: might be less than n) :43 f {S Tn \f “\Lfi IikC-L \/ IS SP-‘rnnLc/ _..| ---‘- "4 .1, v --* A _L 3 l/ V}; “7 Vt ) ’hm X = lel +CLVL+ ....+CK\/K) gr SH“: CUCA’N’ Ck/ JM‘ 2 :firétfi+-~+Lk7lm) ...J :c-xA‘VI+"'+CKA—VKJ (\va 37mm. 'Vxe. an; 4*” etherwud‘ors 'Cnr A (Sdeaer Hm mPe—d‘z’t EBMMIWS TL!» A324: :- C- (IQ-713+“ + Cde‘VK-J :(ICW + --- 5:, {3 aka «2 )MW mmhiha‘fiam 6? flat 72/ Sa :5 flISo I; V Question 8. (8 points total) (a) (4 points) Given that (x — 1)(x — 2)(x — 3) = x3 — 6x2 + 11x — 6 , find all solutions to the differential equation 2f"—12f'+22f’ = 12f S», sake. al—‘"’-11F“+A>A"—m£=aJ or F"—él-‘"+IlJF'—6\C he, dmrm-luaH-A Poljmmt‘ql A: 7;“; )ltml. Jficflmlgl fifwfin :3. ><3— éscnux —<—3/ “In mtg 1,1, all 3 (3.1“ L3 m annual); 5.. 5L 3qu( hum" LS jI-fl 5 it: 3t (93 Rd=C.E’__ +C3_E‘_ FCBE. 4;, coal, ca mm: (b) (4 points) Find the solution to the differential equation in part (a) such that f (O) = 2, f '(0) = 2 and f"(0):=0. ( t. It: 3? [/lthj £2.45): g9; +<;_,_Q, + (3%; I 3L1: 3?:— D‘Qn- Clfiti—lC-LQ’ +3C—3Q’ M:- 31‘ {wit} = C'Qt +Hc3~E +7 C31 ants 90) = (—l + CA'l' I l -"-T C: + M3f¥ 3C3 = l Fall/O) -.": C... “rt-1C; 'l" :0 Question 9. (10 points total) 0 1 Let A = [ b ] where b and c are real numbers. Consider the continuous dynamical system — — c E = A; d! (a) (4 points) What inequality involving 2: and c ensures that the solution to the system will have a phase portrait composed of trajectories spiraling inwards towards the origin? anfl-sil'br-i'la'c. Pblew-miml : 9L1" IL - 1: +59 _¢ 1 CL__|.{L L PLfifl-i. looks ll'lce @ flr‘ww‘l SP-T‘Hlllfi‘j foam-J3 cur-jun) “ugh-ELL real Pal-Cf) Eijmmlwld m1. HLQA 1.3.; USQNUAIM‘S tau—c. “Miami 50 Q; — < 0/ a“) C. i) o 9.“;6 hf: 2 (a) (6 points) Solve this continuous dynamical system ifb = 4, C = 5’ and 55(0) : [ 1] (your answer should be a closed formula for 56(0) 30 wt.— NJ 'l-o L-‘amu-Juej ‘. “Ci ‘1‘75 ___-$”t lr'ie'. Question 10. (6 points total) Find a symmetric 2 x 2 matrix, A, with the following properties: 3 (i) f = [1] is an eigenvector forA (ii) the sum of the two eigenvalues of A equals 0 (iii) the determinant of A equals -1. 11m Sun“ 0-? ttjtfiuqfuq S c) ‘Mphes k') *- k Cnf —“= - I‘MPL'ES l‘C -=r “ k1 {a k .s 1 .F - z, a“ GM, sailing 1’ ENAIQL: I _.__ —_ QAJA_' M j mus (m «or-1 -l / 3H3] end-Jove. -‘-' - 1' ...
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21b Final Fall 2002 solutions - Name: 1 2n Snug/d kg 1 Math...

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