Linear Algebra
Exercises and Problems
1. Determine a basis of Im(f) and of Ker( ) in each of the following cases.f
(a)
f : R
2
R
2
, ( )x
1
, x
2
) 7→ (x
1
+ x
2
, x
1
2x
2
(b)
f : R
3
R
2
, (x
1
, x , x
2 3
) 7→ (x
1
x x
2
3
, 0)
(c)
f : R
2
R
3
, ( )x
1
, x
2
) 7→ (x
1
+ x
2
, 0, x
1
x
2
(d)
f : R
3
R
2
, (x
1
, x , x
2 3
) 7→ (x
1
+ 2 + 3 )x
2
x x x
3
, x
1
2
3
(e)
f : R
4
R
4
, ( )x
1
, x , x , x
2 3 4
) 7→ (x
4
, x , x , x
3 2 1
2. In Exercise 1, which linear mapping is injective, surjective, bijective?
3.
Let
f
:
V W
be a linear mapping and
W
0
a subspace of
W
. Show that
f
1
(
W
0
) is a
subspace of .V
4. Solve the following systems of simultaneous linear equations.
(a)
2x + 3 + 3 9y z =
3 4x y + z = 5
(b)
x + 2y z = 2
x + 4y 3z = 3
(c)
x x x
1
x
2
+
3
4
= 1
x x x x
1
+
2
+
3
+
4
= 2
x x x
1
+
2
x
3
+
4
= 3
(d)
x
1
+ x x
2
+ 2x
3
4
= 4
3x x
2
3
+ 4x
4
= 2
x
1
+ 2x x x
2
3
3
+ 5
4
= 0
5.
Let there be given a linear mapping
f
:
V W
. Show that if
dim dimV > W
then
f
is not injective.
6.
Let
f
:
V W
be an injective linear mapping. Suppose that
{~x
1
, . . . , ~x
k
}
are linearly
independent vectors in
V
. Show that
{f
(
~x
1
)
, . . . , f
(
~x
k
)
}
are linearly independent
vectors in .W
7. Show that if
f : R R
4
2
is a linear mapping so that
Ker(
f) = {(x
1
, x , x , x
2 3 4
) R
4
: x
1
= 5 = 7x
2
, x
3
x
4
},
then f is surjective.
8.
Let
f
:
P
1
R
be a linear map given by
f
(
P
) =
P
(1). Find the image and kernel of
f. Show a basis for each of them.
1

Preview text:

Linear Algebra Exercises and Problems
1. Determine a basis of Im(f ) and of Ker(f ) in each of the following cases.
(a) f : R2 → R2, (x1, x2) 7→ (x1 + x2, x1 − 2x2)
(b) f : R3 → R2, (x1, x2, x3) 7→ (x1 − x2 − x3, 0)
(c) f : R2 → R3, (x1, x2) 7→ (x1 + x2, 0, x1 − x2)
(d) f : R3 → R2, (x1, x2, x3) 7→ (x1 + 2x2 + 3x3, x1 − x2 − x3)
(e) f : R4 → R4, (x1, x2, x3, x4) 7→ (x4, x3, x2, x1)
2. In Exercise 1, which linear mapping is injective, surjective, bijective?
3. Let f : V → W be a linear mapping and W 0 a subspace of W . Show that f −1(W 0) is a subspace of V .
4. Solve the following systems of simultaneous linear equations.  −2x + 3y + 3z = −9 (a) 3x − 4y + z = 5  x + 2y − z = 2 (b) x + 4y − 3z = 3  x1 − x2 + x3 − x4 = 1  (c) −x1 + x2 + x3 + x4 = 2  x1 + x2 − x3 + x4 = 3  x1 + x2 + 2x3 − x4 = 4  (d) 3x2 − x3 + 4x4 = 2  x1 + 2x2 − 3x3 + 5x4 = 0
5. Let there be given a linear mapping f : V → W . Show that if dim V > dim W then f is not injective.
6. Let f : V → W be an injective linear mapping. Suppose that {~x1, . . . , ~xk} are linearly
independent vectors in V . Show that {f ( ~x1), . . . , f(~xk)} are linearly independent vectors in W .
7. Show that if f : R4 → R2 is a linear mapping so that
Ker(f ) = {(x1, x2, x3, x4) ∈ R4 : x1 = 5x2, x3 = 7x4}, then f is surjective.
8. Let f : P1 → R be a linear map given by f(P ) = P (1). Find the image and kernel of
f . Show a basis for each of them. 1