# Result by xiaohuicaicai

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```									Result
If m > n then any set of m vectors in Rn is linearly dependent.
Result
If m > n then any set of m vectors in Rn is linearly dependent.

Basis: Let S be a subspace of Rn and B ⊆ S. Then B is said to
be a basis for S iff B is linearly independent and span(B) = S.
Result
If m > n then any set of m vectors in Rn is linearly dependent.

Basis: Let S be a subspace of Rn and B ⊆ S. Then B is said to
be a basis for S iff B is linearly independent and span(B) = S.

The set {1} is a basis for R1 (= R).
Result
If m > n then any set of m vectors in Rn is linearly dependent.

Basis: Let S be a subspace of Rn and B ⊆ S. Then B is said to
be a basis for S iff B is linearly independent and span(B) = S.

The set {1} is a basis for R1 (= R).

If ei = [0, . . . , 0, 1, 0, . . . , 0]t , where 1 is at the i-th entry and
the other entries are zero, then {e1 , e2 , . . . , en } is a basis
for Rn .
Result
If m > n then any set of m vectors in Rn is linearly dependent.

Basis: Let S be a subspace of Rn and B ⊆ S. Then B is said to
be a basis for S iff B is linearly independent and span(B) = S.

The set {1} is a basis for R1 (= R).

If ei = [0, . . . , 0, 1, 0, . . . , 0]t , where 1 is at the i-th entry and
the other entries are zero, then {e1 , e2 , . . . , en } is a basis
for Rn .

The vectors ei (for i = 1, 2, . . . , n) are called the standard
unit vector.
Example
Find a basis for the subspace S = {x ∈ R4 : Ax = 0}, where
                 
1 −1 −1 2
A =  2 −2 −1 3  .
−1    1 −1 0
Example
Find a basis for the subspace S = {x ∈ R4 : Ax = 0}, where
                 
1 −1 −1 2
A =  2 −2 −1 3  .
−1    1 −1 0

Result
Let S be a subspace of Rn . Then S has a basis and any two
bases for S have the same number of elements.
Example
Find a basis for the subspace S = {x ∈ R4 : Ax = 0}, where
                 
1 −1 −1 2
A =  2 −2 −1 3  .
−1    1 −1 0

Result
Let S be a subspace of Rn . Then S has a basis and any two
bases for S have the same number of elements.

Dimension: The number of elements in a basis for S (a
subspace of Rn ) is called the dimension, denoted dim(S), of S.
Example
Find a basis for the subspace S = {x ∈ R4 : Ax = 0}, where
                 
1 −1 −1 2
A =  2 −2 −1 3  .
−1    1 −1 0

Result
Let S be a subspace of Rn . Then S has a basis and any two
bases for S have the same number of elements.

Dimension: The number of elements in a basis for S (a
subspace of Rn ) is called the dimension, denoted dim(S), of S.

dim(Rn ) = n.
Method of Induction: [Version I]
Method of Induction: [Version I]

Let P(n) be a mathematical statement based on all
positive integers n.
Method of Induction: [Version I]

Let P(n) be a mathematical statement based on all
positive integers n.

Suppose that P(1) is true.
Method of Induction: [Version I]

Let P(n) be a mathematical statement based on all
positive integers n.

Suppose that P(1) is true.

For k ≥ 2, suppose P(k) is true implies that P(k + 1) is
also true.
Method of Induction: [Version I]

Let P(n) be a mathematical statement based on all
positive integers n.

Suppose that P(1) is true.

For k ≥ 2, suppose P(k) is true implies that P(k + 1) is
also true.

Then the statement P(n) is true for all positive integers.
Method of Induction: [Version II]
Method of Induction: [Version II]

Let i be an integer.
Method of Induction: [Version II]

Let i be an integer.

Let P(n) be a mathematical statement based on all
integers n of the set {i, i + 1, i + 2, . . . . . .}.
Method of Induction: [Version II]

Let i be an integer.

Let P(n) be a mathematical statement based on all
integers n of the set {i, i + 1, i + 2, . . . . . .}.

Suppose that P(i) is true.
Method of Induction: [Version II]

Let i be an integer.

Let P(n) be a mathematical statement based on all
integers n of the set {i, i + 1, i + 2, . . . . . .}.

Suppose that P(i) is true.

For k ≥ i + 1, suppose P(k) is true implies that P(k + 1) is
also true.
Method of Induction: [Version II]

Let i be an integer.

Let P(n) be a mathematical statement based on all
integers n of the set {i, i + 1, i + 2, . . . . . .}.

Suppose that P(i) is true.

For k ≥ i + 1, suppose P(k) is true implies that P(k + 1) is
also true.

Then the statement P(n) is true for all integers of the set
{i, i + 1, i + 2, . . . . . .}.
Matrices
Matrices

Deﬁnition: Let A = [aij ] be an m × n matrix.
Matrices

Deﬁnition: Let A = [aij ] be an m × n matrix.

If m = n, then A is called a square matrix.
Matrices

Deﬁnition: Let A = [aij ] be an m × n matrix.

If m = n, then A is called a square matrix.

If A is a square matrix, then the entries aii are called the
diagonal entries of A.
Matrices

Deﬁnition: Let A = [aij ] be an m × n matrix.

If m = n, then A is called a square matrix.

If A is a square matrix, then the entries aii are called the
diagonal entries of A.

If A is a square matrix and if aij = 0 for all i = j, then A is
called a diagonal matrix.
Matrices

Deﬁnition: Let A = [aij ] be an m × n matrix.

If m = n, then A is called a square matrix.

If A is a square matrix, then the entries aii are called the
diagonal entries of A.

If A is a square matrix and if aij = 0 for all i = j, then A is
called a diagonal matrix.

If an n × n diagonal matrix has all diagonal entries equal to
1, then it is called the identity matrix of size n, and is
denoted by In (or simply by I).
Matrices

Deﬁnition: Let A = [aij ] be an m × n matrix.

If m = n, then A is called a square matrix.

If A is a square matrix, then the entries aii are called the
diagonal entries of A.

If A is a square matrix and if aij = 0 for all i = j, then A is
called a diagonal matrix.

If an n × n diagonal matrix has all diagonal entries equal to
1, then it is called the identity matrix of size n, and is
denoted by In (or simply by I).

If all the entries of A are equal to 0 then A is called a zero
matrix, denoted Om×n (or simply by O)
A matrix B is said to be a sub matrix of A if B is obtained
by deleting some rows and/or columns of A.
A matrix B is said to be a sub matrix of A if B is obtained
by deleting some rows and/or columns of A.

The transpose At of A = [aij ] is deﬁned as At = [bji ], where
bji = aij for all i, j.
A matrix B is said to be a sub matrix of A if B is obtained
by deleting some rows and/or columns of A.

The transpose At of A = [aij ] is deﬁned as At = [bji ], where
bji = aij for all i, j.

The matrix A is said to be symmetric if At = A.
A matrix B is said to be a sub matrix of A if B is obtained
by deleting some rows and/or columns of A.

The transpose At of A = [aij ] is deﬁned as At = [bji ], where
bji = aij for all i, j.

The matrix A is said to be symmetric if At = A.

The matrix A is said to be anti-symmetric (or
skew-symmetric) if At = −A.
A matrix B is said to be a sub matrix of A if B is obtained
by deleting some rows and/or columns of A.

The transpose At of A = [aij ] is deﬁned as At = [bji ], where
bji = aij for all i, j.

The matrix A is said to be symmetric if At = A.

The matrix A is said to be anti-symmetric (or
skew-symmetric) if At = −A.
t
If A is a complex matrix, then A = [aij ] and A∗ = A .
A matrix B is said to be a sub matrix of A if B is obtained
by deleting some rows and/or columns of A.

The transpose At of A = [aij ] is deﬁned as At = [bji ], where
bji = aij for all i, j.

The matrix A is said to be symmetric if At = A.

The matrix A is said to be anti-symmetric (or
skew-symmetric) if At = −A.
t
If A is a complex matrix, then A = [aij ] and A∗ = A .

The matrix A∗ is called the conjugate transpose of A.
A matrix B is said to be a sub matrix of A if B is obtained
by deleting some rows and/or columns of A.

The transpose At of A = [aij ] is deﬁned as At = [bji ], where
bji = aij for all i, j.

The matrix A is said to be symmetric if At = A.

The matrix A is said to be anti-symmetric (or
skew-symmetric) if At = −A.
t
If A is a complex matrix, then A = [aij ] and A∗ = A .

The matrix A∗ is called the conjugate transpose of A.

The (complex) matrix A is said to be Hermitian if A∗ = A,
and skew-Hermitian if A∗ = −A.
A square matrix A is said to be upper triangular if aij = 0
for all i > j.
A square matrix A is said to be upper triangular if aij = 0
for all i > j.

A square matrix A is said to be lower triangular if aij = 0 for
all i < j.
A square matrix A is said to be upper triangular if aij = 0
for all i > j.

A square matrix A is said to be lower triangular if aij = 0 for
all i < j.

Let A be an n × n square matrix. Then we deﬁne
A0 = In , A1 = A and A2 = AA.
A square matrix A is said to be upper triangular if aij = 0
for all i > j.

A square matrix A is said to be lower triangular if aij = 0 for
all i < j.

Let A be an n × n square matrix. Then we deﬁne
A0 = In , A1 = A and A2 = AA.

In general, if k is a positive integer, we deﬁne the power Ak
as follows
Ak = AA . . . A .
k times
A square matrix A is said to be upper triangular if aij = 0
for all i > j.

A square matrix A is said to be lower triangular if aij = 0 for
all i < j.

Let A be an n × n square matrix. Then we deﬁne
A0 = In , A1 = A and A2 = AA.

In general, if k is a positive integer, we deﬁne the power Ak
as follows
Ak = AA . . . A .
k times

If A and O are matrices of the same size, then
A + O = A = O + A, A − O = A, O − A = −A, A − A = O.

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