Mathematics IB Tutorial 5
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Mathematics IB Tutorial 5
1. Let F : R2 → R3 be defined by F (x, y) = (y, x + y, 2x), and let G : R3 → R2 be defined by G(x, y, z) = (z, x + y).
(a) Find formulae for each of F 。G and G 。F by directly composing
the functions.
(b) Find standard matrices of F ,G, F。G and G。F and hence confirm
your results from the first part.
(c) Let H : R2 → R2 be a linear transformation defined by rotation
π
2. For the two series
& 2k
k! k=2
and (b) & (-1)n n3
n=1
what tests would be appropriate for deciding whether each series in convergent? Apply them. [Hint: if f(n) = n /(n34 + 1), what is the sign of f\ (n)?]
Practice Questions
Algebra
1. Let F : R3 → R4 be a linear transformation which satisfies F (1, 0, 0) = (-2, -4, -4, 0), F (2, 0, 1) = (-1, -2, -2, 2) and F (0, 2, 1) = (-6, -2, 0, 4).
(a) Find the standard matrix of F .
(b) Find the kernel and range of F .
2. Let F : R3 → R3 be a linear transformation which has a standard ma- trix which is diagonal. If F (1, 2, 3) = (5, 10, 4) then what is F (4, 5, 6)?
3. Let F : R3 → R2 be the linear transformation F (x, y, z) = (x, y + z) and let G : R2 → R3 be defined by G(1, 0) = (0, 1, 2) and G(0, 1) = (0, 2, 0).
(a) Find the standard matrix of the composition G 。F .
(b) Find the kernel and range of G 。F .
(c) Find the standard matrix of the composition F 。G.
(d) Find the kernel and range of F 。G.
4. Let F : R2 → R2 be (anticlockwise) rotation by , let G : R2 → R2 be a reflection in the x-axis and H : R2 → R2 be a dilation by a factor of ^8 (ie a dilation with t = ^8). Find the standard matrix for each of the following linear transformations:
(a) F 。H 。G
(b) F 。G 。H
(c) H 。G 。F .
5. (a) Prove that that there is no linear transformation F : R3 → R3 such that ker(F) = R(F).
(b) Find a linear transformation F : R2 → R2 such that ker(F) =
R(F). You must explicitly show that your example has this prop- erty.
6. Let F : Rl → Rm and G : Rm → Rn be linear transformations.
(a) Show that ker(F) S ker(G 。F).
(b) Show that R(G 。F) S R(G).
7. Prove that a linear transformation F : Rn → Rn is invertible if and only if ker F = {6}.
8. (a) Find the standard matrix A of the linear transformation F rep- resenting the cyclic permutation
F (x1 , x2 , x3 , x4 ) = (x4 , x1 , x2 , x3 ).
(b) What is the effect of the composition F。F? What is the standard
matrix for F 。F?
(c) Show that A3 = A一1 . Why would you have expected this for the standard matrix of F?
(d) Is F invertible? Explain.
9. [Non- examinable challenge] Let A and B be n x n matrices, and suppose that there exists some invertible n x n matrix such that A = P一1 BP . In this case A and B are called similar matrices. Prove that any two similar matrices have the same rank. (Note that to do this you only need techniques from Section 2 of the course, but the result is important for the theory of linear transformations).
10. [Non- examinable challenge] The set L(Rn , Rm ) of linear transforma- tions from Rn to Rm is itself a vector space. Let F, G : Rn → Rm be linear transformations, and k e R, then we define (F + G)(u) = F (u) + G(u) and (kF)(u) = kF (u).
(a) Show that {F, G, H} is a linearly dependent set in L(R2 , R2),
where F (x, y) = (y, x),
G(x, y) = (x + y, x - y) and H(x, y) = (y - 2x, x + 2y).
(b) Describe a basis for the vector space L(R2 , R2) of all linear trans- formations from R2 to R2 .
(c) Is the subset of invertible transformations a subspace of L(R2 , R2)?
(d) [Extra- challenging!] Define a map T : L(R2 , R2) → R2 by T (F) = F (e1 ) - F (e2 ), where {e1 , e2 } is the standard basis for R2 . Prove that T is a linear transformation and find the Kernel and the Range of T.
Calculus
Series
11. Explain the difference between
n n
(a) ai and aj
i=1 j=1
n n
(b) ai and aj
i=1 i=1
i j
(c) an and an n=1 n=1
12. Do the following series converge or diverge? Provide explanations.
&
1
n
&
3
j - 1
&
(c) 2n n=3
(d) n ╱ 、 n
13. By utilising the fact that you know the sum of a geometric series, find the explicit values of each of the following series.
& (-1)n
4n
n=0
& 2n+1
5n
n=2
& 3n一1 - 1
6n一1
n=1
14. Determine the following repeating decimals in rational form by using a geometric sequence.
(a) 0.1233333 . . .
(b) 0.0454545 . . .
15. In this problem, we learn the ‘telescoping sum’ process to determine certain types of infinite sums.
&
(a) For the series , use partial fractions to show that the
n(n + 1) n n + 1 .
(b) Hence, observe that the partial sums sm obey
sm := n = n ╱ - 、
= ╱ - 、 + ╱ - 、 + ╱ - 、 + . . . + ╱ - 、 + ╱ - 、 = 1 -
because the intermediate terms cancel with adjacent terms (the
sum collapses like a telescope). By determining lim sm, deter-
&
1
n(n + 1) .
n=1
&
(c) Use this telescoping sum idea to determine the sum n=2
2 |
n2 - 1 . |
(d) [Non- examinable challenge] Use this idea to also determine the
&
3
n(n + 3) .
n=1
16. Do the following series converge or diverge? Provide explanations.
&
1
^n
n=2
& (-1)n
n
2n2 + n + 7
n=1
17. By comparing with a known series, show that each of the following series converges.
&
1
n2 + 10
& sin2 n
3
&
1
n2n
n=1
18. Use the ratio test to determine whether each of the following series converge.
&
(a)
n=1
2k!
(2k)!
k=1
19. Apply the ratio test to each of the following series to investigate con- vergence.
(a) & (-1)n
n=1
&
(b)
&
(c) , where p e R.
20. We have shown in lectures and course notes that the harmonic series diverges. It turns out that the partial sums sn of the harmonic series diverge about as fast as ln n. To test this, consider the sequence
bn := sn - ln n := ╱ + + + . . . + 、 - ln n .
The quantity V := lim bn is an important mathematical constant
known as Euler’s constant. Write a Matlab code to generate the se- quence {bn}. By computing bn for as large a value of n as necessary, determine V correct to four decimal places.
2022-09-02