MATH2069 Mathematics 2A Term Three 2020
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Term Three 2020
MATH2069
Mathematics 2A
Submit solutions to this question at the Q1 submission link
1. [20 marks]
i) [5 marks] Consider a particle traveling in R3 along the curve r(t) = 12ti . t3j + (t2 + 4t)k, t e R.
a) Find the velocity and acceleration of the particle (as functions of t).
b) Find all points where the velocity of the particle is perpendicular to the plane x = y .
ii) [5 marks] Use the method of Lagrange multipliers to find the minimum value of x + 2(y + z) on the sphere x2 + y2 + z2 = 36.
iii) [6 marks] Let h(x, y) be a differentiable function. Suppose that at the point (0, 1), the directional derivative of h in the direction i + j is 2^2 and the directional derivative of h in the direction i . j is .^2.
a) Find the gradient of h at (0, 1).
b) Find the directional derivative of h at (0, 1) in the direction i + 2j.
c) What is the maximum value of the directional derivative of h at (0, 1), in any direction?
iv) [4 marks] Consider the sum of integrals
4 ^α 8 ^8尸α
f(x, y) dy dx + f(x, y) dy dx
0 尸^α 4 尸^8尸α
a) Sketch the region of integration.
b) By reversing the order of integration, write the sum of integrals as a single integral.
Submit solutions to this question at the Q2 submission link
2. [20 marks]
i) [6 marks] Let
S1 = {z e C : 0 < Arg z < }
S2 = {z e C : |z . 1| < 1}
a) Sketch S1 and S2 on separate Argand diagrams and for each set state if it is a domain. Motivate your answer.
b) Find and sketch the image of S1 under the mapping w = z2 .
c) Find and sketch the image of S2 under the mapping w = 1
ii) [3 marks]
a) Express (^3 . i)2i in Cartesian form.
b) Hence, write Re(p.v.(^3 . i)2i).
iii) [7 marks] Suppose that
f(z) =
5 |
(z . 2)(z + 3) . |
a) Sketch and write down the three (maximal) regions with centre at z = .2 on which f(z) has a convergent Laurent (or Taylor) expansion in powers of z + 2.
b) Find the Laurent series expansion of f in powers of z + 2 which is convergent at the point z = 1.
iv) [4 marks]
a) Let γ be the line segment from .i to 2. Evaluate & ( . 1) dz and express the result in Cartesian form.
b) Let now Γ be any contour from .i to 2. Using the fundamental theorem of contour integration, evaluate Γ sinh(2z)dz and express
the result in Cartesian form.
Submit solutions to this question at the Q3 submission link
3. [20 marks]
i) [5 marks] Use a change of variables to find the area of the region in the
first quadrant of the xy-plane that is bounded by the curves xy = 2, xy = 3, x = y, x = 4y .
ii) [5 marks] Consider the solid region in the first octant of R3 that is
● between the planes y = 0 and y = x;
● bounded above by the cone z = 2^x2 + y2 ;
● and inside the cylinder x2 + y2 = 1;
Set up a triple integral in spherical coordinates which gives the volume of this region.
(Do NOT evaluate the integral).
iii) [4 marks] Let S be the surface in R3 defined by the equation z = xy2 . Let Ω be the region in the first quadrant of the xy-plane bounded by the coordinate axes and the circle x2 + y2 = 4. Set up a double integral which
gives the surface area of the part of S above Ω .
(Do NOT evaluate the integral).
iv) [6 marks] Let C be the circle in R3 which is the intersection of the cylinder x2 + y2 = 1 with the plane z = 2. Let C be oriented clockwise,
when looking down from the positive z-axis. Consider the vector field F = (x3 + 2yz)i + (5xz + e女扌 )j + cosh(xy + z)k.
a) Calculate the component of the curl of F in the k direction.
b) Let S be the disk whose boundary circle is C . Parametrize S, and find the corresponding normal vector at each point of S . (Note that the normal vector of a parametrisation is determined up to a sign).
c) Use Stokes’ Theorem to evaluate the line integral F · dr. C
(Hint: you should not have to do any complicated integration)
d) Without doing any further calculation: is there a scalar function φ : R3 → R such that F = Vφ? Explain.
Submit solutions to this question at the Q4 submission link
4. [20 marks]
i) [6 marks] Given that the function u : R2 → R defined by u(x, y) = .2 sinh x cos y + y3 . 3x2y
is harmonic (you do not need to prove this):
a) Find a harmonic conjugate v for u.
b) Let f (x + iy) = u(x, y) + iv(x, y) for all x, y e R, for the function v found in the previous part. Find f (z) as a function of z alone.
ii) [7 marks] Suppose that
cosh(πz)
g(z) =
Let Γ denote the circle with centre at 0 and radius 2, traversed in the anticlockwise direction.
a) Find and classify all singularities of g, justifying your answers.
b) Determine the residues of g at z = i and z = 3i.
c) Hence, or otherwise, calculate the integral
g(z)dz .
Γ
iii) [7 marks] Use complex analysis methods to find
′ cos 2x
x2 . 4x + 5
sin 2x
x2 . 4x + 5
2022-11-23