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Linear Algebra Notes (Reformatted)

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A re-upload of class notes taken in an undergraduate Linear Algebra prerequisite course. Covering the basics of linear algebra including: - Vectors - Vector Spaces - Matrices (and Augmented Matrices) - Matrix Operations (including Matrix Multiplication) - Row Reduction - Solution Sets (and Set Builder Notation) - Homogeneous Solution Sets - Rank and Rank Space - Null Space - Rank-Nullity Theorem

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I




Linear Combinations of Vanables


C X,6
,
CXcb . . . CnXn C= I In each row of a liver system , the first nu-zers


term is called the leading -able
A liner equation in neveriables has the form

* lineer system is
in echelon form if the /
d 23d IR
2X , 0Xb 62Xn =
in each is to the right of the leading verable
... =

, ,
now


in the preceding equation

* lineer system neveriables has the form : Goal echelon form using
in :
Augmented matrix into now
operations
.




Due echelon form substitutions
in
, you can do algebraic
a X +9 24 ... +a
, nXn = d ↓ solve for all variables
provided that there is
, , , , , ,


2
c ,,
X
,
6 az , 2X26 ...
+az ,
nXn =
da a solution

&
k ,, X ,
+
9 2
X
<b
...

+ak nXn = dk
, ,




Definition .
A set S is a collection of objects called
We say an notuple (S
,,
Sc
,
"Sn) is a solution the elements or members .




previous liner system if it solves each equation
.




The set of all real numbers is denoted
R
Definition. Al"real") matrix is a kxn array of
real ↳ S2 is a real number so can be shown
,



numbers (K rors
,
n columns) "SER"

An matrix whose last "T2-IR" translates to 52
aumented is a matrix is an



column represents the constants in a
line system an element/member of the real .
number set

and whos first in columns represent the

offerent in an n-variable linear system Set builder notation
↳ set :
you can describe all elements in a


Theorem Gauss' Method


Formula inton
.




↓ liner system can be
changed to another by one s =
E
of these operations
1) Our equation swapped with another canplya
) One equation
2
multiplied by is a non-zero scaler

3) An equation is replaced with the sum of itself is s =

3 I 3
a sealer multiple of another equation
un un

element your'e property of element
Definition These operations selected
.
or called now operations, selecting
elementaryrow operations ,
or Gaussian Operations.

,2




Examples .
S =
G1 ,
2
,
4
, 83 Add metirees of same size
,
entry by entry



32" /k 33
(i)(iii)
S =
= 0 1
,
2
, .




S =
ExtR/x is
rational]
S29S
-(12) is)
Definition .
Variables (in echelon form) that be
not a Subtract likewise

leading variable are a free viable.


Scale multiplation ,
let I be a sealer


(213)
x = 7z +
02:1 A
Icacalist
H X -
-zo4

3)70)02 = 1
2(4) :

(ii)
33367 = 1


** You can multiply 2 mutrices A B ,
if

Na
=
k or Ka =
NB



() A .




I 123)B
456
=




( ))
,




2 +3




3)(ii) 1 2 3
3x/
=


AB =


(13 1)02 (5) =




If a matrix has n rows and K columns we
,


can write :




A Suppose A




(
is mabrix B



&
nxk and kXm

alia
an is a


matrix
.
The product of As B will be an nxm matrix
AB C let hij be the entry in the ith

an
=

column
---

now
,
i
and column of C
an ,
1 an
,
2 ...

jth

between Cij dot product of the ith of A and the
add double digit indices.
=
* a commu
now



of B
jth now

,3




GausCordan EliminationRedmedchelonFoa 16 : 3) ↳ & 3 no solutions
,


if addition echelon form
,
in
to
being in




#85 )
each leading entry is
I and is
%

the only nonzwo entry in its
column 1 pirot free
.
,
y3z are variables

Definition . The
leading entry is also called a pirot ↳ Infinite solutions



Example.
Definition. A linear equation is
homogeneous if it has a




I (ii)
I 2 constant term of A lime
zero.
system is

·
J
homogenous if every exaction is homogeneous .



O
oooo
makethisleabo
X +
y + 2z = 0




I I
.
it X +
Y 27 = 0

X
-
37 = 0




im
pivot is I
,
and is the only non-zero entry & 2
,
9 0
, ... Gal e
, ... ER3
in
its column .




Where I is a
particula solution to the lime system
Non-example -



Example and where the number of rectors (B) is equal




.




%]
to the # of free voiables the system has

after Gaussian Reduction




Lemme.
For any homogeneous system there exists
,


Note . vectors Bi such that the solution set
has the formi

# of free voiables

& , , ... ,
... -R3
↳ If there is at leastI free vorable in a


has Whoe K is the number of free veciables after
system with no contradictions , then the system
solutions Gaussian Reduction
infinitely many

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Uploaded on
August 19, 2026
Number of pages
18
Written in
2023/2024
Type
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Stefanie wang
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