Linear Algebra Exercise Solutions for Spring 2023 - Prof. Jay Shapiro, Exams of Linear Algebra

Solutions to various exercises from a linear algebra course during the spring 2023 semester. Topics covered include determining linear dependence, one-to-one transformations, invertible matrices, and finding determinants. Students are advised to work carefully and neatly, and no notes, books, or calculators are allowed.

Typology: Exams

2010/2011

Uploaded on 07/20/2011

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Math 203 Spring Z}1-l-Exarn 2
Instructor: Shaoiro
Work careftrlly and neatly and remember that I cannot gracle what I cannot read. You
must show all relevant work in the appropriate space. You rnay receive 1o credit for a correct
allswer if there is insufficient supporting lvork. Notes, books ancl graphing or prograrnable
ci-ilculators are NOT ALLOWED.
[21prtl 1. Fill in the blanks with,4 (Iways), S(ometi'mes). N(e,uer)so that the followirlg ar.e correct
stal,eurents.
(a) If A is a 3 x 5 matrix, then the columns of A u.. A linearly dependent.
(b) If A is a3 x 2 matrix, then the transformationxp+,4x is S one-to-one.
(c) If the rnatrix B is obtained frorn A by adding three times the first row to the third
t'ow of A. then lAl 5/ t', equals 3lBl.
(d) If A is invet'tible n x n matrix, then the matrix equation Ax : b, rvhere b is any
ru-tr.rple, A has a unique solutiou.
(e) If ,4 is a non-invertible square matrix, then the columns of A are A linearly
independent.
(f) If A is a 5 x 5 invertible rnatrix, then lAl S equals 2b.
(g) If ,4 is a scluare invertible matrix and B is obtained from ,4 by perforrning a sequelce
of stanclard elementary row operations on ,4, theu B is A invertible.
u) lA-'l b) l3Al c) 2a 2b 2c
3a*d 3b*e 3c+ f
shi
= j1 'f r ).{= ?
[15pt] 2. Let o:f i 2 ;land lAl : 4. compute the following determinants:
lg h i)
b-!
.?
pf3

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Y

Math (^203) Spring Z}1-l-Exarn (^2)

Instructor: Shaoiro

Work careftrlly and neatly and (^) remember that I (^) cannot gracle (^) what (^) I cannot read. You must show (^) all relevant work (^) in the appropriate (^) space. You rnay (^) receive 1o credit for a correct

allswer if there is insufficient supporting lvork. Notes, books ancl graphing or prograrnable

ci-ilculators are (^) NOT ALLOWED.

[21prtl 1.^ Fill^ in^ the^ blanks^ with,4^ (Iways), S(ometi'mes). N(e,uer)so that the followirlg ar.e correct

stal,eurents. (a) If (^) A is a 3 x 5 matrix, (^) then the columns (^) of A u.. A (^) linearly (^) dependent. (b) If A (^) is a3 x 2 matrix, then the transformationxp+,4x (^) is S (^) one-to-one.

(c) If the rnatrix B is obtained frorn A by adding three times the first row to the third

t'ow of A. then (^) lAl 5/^ t',^ equals 3lBl. (d) (^) If A is invet'tible (^) n x n matrix, (^) then the matrix equation (^) Ax : (^) b, rvhere b is any ru-tr.rple, (^) A has (^) a unique solutiou. (e) If (^) ,4 is a non-invertible (^) square matrix, then the columns (^) of A are A (^) linearly independent.

(f) If A is a 5 x 5 invertible rnatrix, then

lAl S^ equals^ 2b.

(g) If ,4 is a scluare invertible matrix and B is obtained from ,4 by perforrning a sequelce

of stanclard elementary (^) row operations on ,4, theu B is (^) A invertible. u) (^) lA-'l b) (^) l3Al c) 2a 2b (^) 2c 3ad 3be (^) 3c+ (^) f shi = j1 (^) 'f r (^) ).{=? [15pt] 2.^ Let^ o:f^ i^2 ;land (^) lAl :^ 4.^ compute^ the following^ determinants: lg h i) b-!.?

(2 2 o o^ F 3 LetA: | 3 ;^3 3 | \o o 2^ r/

(u) Cornpute lAl.

€ tiil lill--

,),r,

s€€€Fd rorv, and 3 times the first row to the tlittfrow).

hrr4 tacod a /to o/roc
/ I \ (^) t o I o ll ar e J: f j \ -i o r / ^ e o^ r I^ \ -l [16pt] ).(r-t") = -

i)

o\

(b) Find .4-l

'lr -t, O Q '-r/., 'l/v

O ,1,^ -^ '/.

-Y

l

u

=tJ | - / |^ b r-- [r/r t
-j -2lY /)-1 ).^ \

w

[.b.];l

I

( (^1 3) -r\ lt s _r
[101;ts] 5.LetA:{-s2^ r f andB:lo^11 -2 I FindamatrixCsrutrthar \ 22 t/^ \o -4 sl CA: B (note^ that B was obtained (^) from A by adding (^) -2 tirnes (^) the first row to the o I I t tr^ t- ,'A

r /'/tr tt

t/ gl-r/^ /

r//(/// fr

\ '///-{t [f 0pt]^ 4.^ Find^ the^ LUfactorization^ of^ U: (^? -o