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Title: TMC1874 Mathematics For Computing tutorial 6 solution
Description: Tutorial Solution Chapter 6: Linear Transformations

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TMC1874 Mathematics For Computing

Tutorial Solution
Chapter 6: Linear Transformations

1
...
Then
L([u 1

u 2 ] + [v1

L([u 1 + v1

=

u1 + u2]

v2 ]),

u 2 + v2 ]),

= [u 1 + v1

u 2 + v2

= [u 1

u 1 + u 2 ] + [v1

u2

u 1 + u 2 + v1 + v2 ],
v2

v1 + v2 ],

L(u) + L(v)

=

and let c be any scalar
...


=

cL(u)
...


(b) L : R2 → R3 defined by L([u 1
Solution
Let u = [u 1

u 2 ]) = [u 1 + u 2

u 2 ] and v = [v1
L(u + v) =

v2 ]
...


and
L(u) + L(v) = [u 1 + u 2

u2

u 2 − 1] + [v1 + v2

= [u 1 + u 2 + v1 + v2
=

u 2 + v2

v2

v2 − 1],

u 2 + v2 − 2],

L(u + v)
...


2
...
]
W
...
Tiong

Page 1 of 7

TMC1874 Mathematics For Computing

(a) L : P1 → P2 defined by L(p(t)) = tp(t) + p(0)
Solution
Let p(t), q(t) be polynomials in P1 and let c be any scalar
...


and
L(c p(t)) = t[c p(t)] + c p(0) = c[tp(t) + p(0)] = cL(p(t))
...


(b) L : P1 → P2 defined by L(p(t)) = tp(t) + 1
Solution
Let p(t), q(t) be polynomials in P1 and let c be any scalar
...

Therefore, L is not a linear transformation
...
Find the standard matrix representing each given linear transformation
...
Compute L(e j ) for j = 1, 2 as follows:
L(e1 ) = L

1
0

L(e2 ) = L

Hence the matrix A = [L(e1 )

W
...
Tiong

L(e2 )] =

−1
0

=

0
1

,

0
1


...


Page 2 of 7

TMC1874 Mathematics For Computing

u1
u2

(b) L : R2 → R2 defined by L

=

u1 − u2
u1

Solution
Let {e1 , e2 } be the natural basis for R2
...


=
=

1
1

L(e2 )] =

−1
0


...
Compute L(e j ) for j = 1, 2, 3 as follows:
 
1
L(e1 ) = L  0  = 
0

 
0
L(e2 ) = L  1  = 


0

0
L(e3 ) = L  0
1


Hence the matrix A = [L(e1 )

L(e2 )


1
0 ,
0

0
0 ,
0
 

0
 =  0 
...
Consider the function L : M34 → M24 defined by L(A) =
1
(a) Find L  3
4


W
...
Tiong

2
0
1

0
2
−2

0
0
0



2
0

0
2


0
0 
...



−1
3 
1

Page 3 of 7

TMC1874 Mathematics For Computing

Solution

1
 3
L
4

2
0
1



0
2
−2


−1
3  =
1

2
0

0
2

6
−6

=

1
 3
4


1
−3
5
−3

−2
10

−1
3

2
0
1

0
2
−2


−1
3 
1


...

Solution
Let M =

2
0

0
2

1
−3


...
Therefore

L(A + B) =
L(c A) =

M(A + B) = M A + MB = L(A) + L(B),
M(c A) = c(M A) = cL(A)
...


5
...



1
(a) What is L  −2 ?
3


Solution


1
L  −2  =
3







1
0
0
L  0  − 2L  1  + 3L  0 
0
0
1


=

1
2

=

2
−3

5
1

12
11

−2

+3


u1
(b) What is L  u 2 ?
u3


W
...
Tiong

Page 4 of 7

TMC1874 Mathematics For Computing

Solution


u1
L  u 2  =
u3


=






1
0
0
u 1 L  0  + u 2 L  1  + u 3 L  0 
0
0
1


u1

1
2

2
−3

+ u2

u 1 + 2u 2 + 5u 3
2u 1 − 3u 2 + u 3

=

u1
u2

6
...


in range L?

(e) Find ker L
...


Solution

(a) L

0
2

=

0
2


...


(b) L

2
0

=

0
0


...


(c) No because

3
0

does not have the form

0
u2


...


(e) The kernel of L consists of all vectors
0
0

u1
u2

u1
u2

such that L

=

0
u2

=


...
Therefore ker L

consists of all vectors

a
0

, where a is any real number
...


W
...
Tiong

Page 5 of 7

TMC1874 Mathematics For Computing

7
...


2] in range L?

(d) Is [0

u2

0] in range L?

−2

− 1] is in ker L?

1] is in ker L?

(e) Find ker L
...


Solution

(a) Yes since L([1

−1

(b) No since L([0 2

1

− 1]) = [0

0]
...


(c) Yes since [1

2] = L([1

2 0

0])
...


This leads to the system of equations u 1 + u 4 = u 2 + u 3 = 0
...
Therefore the kernel
consists of all vectors of the form [r s − s − r], where r and s are real numbers
...
Since u 1 + u 4
and u 2 + u 3 can assume any real value, the range is all vectors [a b] = a[1 0] +
b[0 1]
...


8
...


(a) Find a basis for ker L
...

(d) What is dim range L?

Solution

(a) [u 1 u 2 u 3 u 4] is in the kernel if and only if u 1 + u 3 = u 2 + u 4 = 0
...
Therefore the kernel consists of all vectors of the form [−a −

W
...
Tiong

Page 6 of 7

TMC1874 Mathematics For Computing

b

a

b], where a and b are any real numbers
...


1]}
...

(c) The range consists of all vectors of the form
[u 1 + u 3

u2 + u4

u1 + u3] =

u 1 [1 0
+ u 4 [0

1] + u 2 [0
1

= (u 1 + u 3 )[1

A basis is {[1

0 1], [0

1

0] + u 3 [1

0 1]

0],
0 1] + (u 2 + u 4 )[0

1

0]

1 0]}

(d) dim range L = 2

9
...


(a) Find a basis for ker L
...


Solution
(a) The kernel consists of all polynomials at2 + bt + c such that L(at2 + bt + c) = [a b] =
[0 0]
...
Hence ker L consists of the polynomials c, c any
number
...

(b) The range consists of matrices [a

W
...
Tiong

b] = a[1 0] + b[0 1]
Title: TMC1874 Mathematics For Computing tutorial 6 solution
Description: Tutorial Solution Chapter 6: Linear Transformations