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This is the Exam Key of Applied Linear Algebra which includes Homogeneous Coordinates, Linear Equations, Precise Description, Linearly Independent etc. Key important points are: Linear Combination, Statements, Explanation, Inconsistent, Set Spanned, Homogeneous, Zero Vector, Identity Matrix, Undefined, Compute
Typology: Exams
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. For BA to be defined, the number of columns of B would have to equal
the number of rows of A. This is not the case.
a.
A b
b.
A b
This means that
1 3
2 3
3
x x
x x
x
, or that
1
2
3
x
x x t
x
c.
, and so the set
is not linearly independent.
a. There is no pivot in column 3. This means that the matrix is not row-equivalent to the
identity matrix, and by the Invertible Matrix Theorem, it is not invertible.
b.
8 2 1
3 3 3
17 5 1
3 3 3
5 2 1
3 3 3
And so
8 2 1
3 3 3
1 17 5 1
3 3 3
5 2 1
3 3 3
−
a. A transformation :
n m
T → is said to be linear if
T u + v = T u + T v
T cu = cT u
for all ,
n
u v ∈
and all scalars c ∈ .
b.
1 1 1 1 1 1 2 2 1 2 1 2
2 2 2 2 1 1 2 2 1 2 1 2
1 1
2 2
u v u v u v u v u u v v
u v u v u v u v u u v v
u v
u v
1 1 1 2 1 2 1
2 2 1 2 1 2 2
u cu cu cu u u u
T c T c cT
u cu cu cu u u u
Thus T satisfies the definition in (a), and so T is linear.
1 2
A T e T e
a. A transformation :
n m
T → is said to be one-to-one if whenever u ≠ v
, it follows
that
T u ≠ T v
b. For sufficiency, suppose that
T x = 0
has a non-trivial solution, x = c
. As T is linear,
x = 0
is always a solution to
T x = 0
. Since c ≠ 0
and
( )
T c = T 0 = 0
, T fails to
satisfy the definition of one-to-one.
For necessity, suppose that T is not one-to-one. Then there are vectors ,
n
a b ∈
where
a ≠ b
, but
m
T a = c ∈
and
( )
T b = c
. As a ≠ b
, we have that a − b ≠ 0
. Now
( ) ( ) ( )
T a − b = T a − T b = c − c = 0
has a non-trivial solution.