MAT344: Complex Variables Fall 2022 Homework 1
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MAT344: Complex Variables
Fall 2022
Homework 1
1. Let z be a complex number which satisfies the following equation: z3 + i2 − 3z − 4 = i.
(a) (2 points) Show that z can not be a real number.
1 − 4i
(b) (4 points) Find the modulus of
(c) (4 points) Find the imaginary part of −3 + iz2 + 3 + i.
2. (5 points) For this question, let Arg(z) denote the argument of z lying in [−π,π). For any z 0 lying on the circle |z − 1| = 1, show that Arg(z − 1) = 2Arg(z), and provide a geometric interpretation.
Hint: show that cos(Arg(z − 1)) = cos(2Arg(z)) by applying a double angle formula.
3. Let p be a positive real number and let Γ be the locus of points satisfying |z − p| = cx where z = x + iy , and c ∈ R is a constant.
(a) (4 points) Show that Γ is an ellipse (not necessarily centered at the origin) if 0 < c < 1 (b) (4 points) Show that Γ is a horizontal parabola if c = 1
(c) (2 points) Show that Γ is a hyperbola if c > 1
4. Let A be the strip {z ∈ C : 0 < Re(z), 0 ≤ Im(z) < 2π} and f : C → C be the map given by f(z) = i + e−z .
(a) (3 points) Find the image f(∂A), where ∂A is the boundary of A in C.
(b) (3 points) Show that for every z ∈ A, we have |f(z) − i| < 1.
(c) (4 points) Suppose D is the punctured disk {z ∈ C : 0 < |z − i| < 1}. Show that for every w ∈ D there exits z ∈ A such that f(z) = w and conclude the image f(A) is D .
5. Determine whether the following series converge or diverge. Justify your answer. (a) (5 points) 对
(b) (5 points) 对 where z ∈ C/Z
6. Consider the following limits:
(a) (3 points) Find,
z eπi(m)/3 (z − eiπ/3)
(b) (2 points) Let h(z) = . Determine whether limz →0 h(z) exists.
7. Let a1 ,a2 , . . . an be disinct real numbers, i.e., ak ∈ R for all k and ak aj if k j . Consider the function,
n
ak − z ,
defined for z ∈ C/R.
(a) (3 points) Show that for z in the upper half plane z ∈ H+ = {z = x + iy : x ∈ R,y > 0} we have, Im[f(z)] > 0.
(b) (3 points) Calculate,
limIm[f(x + iy)]
y↓0
for x ∈ R.
(c) (4 points) Show that the limit,
g(x) = limRe[f(x + iy)]
y↓0
exists for every x ∈ R. Is g(x) continuous? Why or why not?
Hint: for (b), (c) consider separately the cases whether x = ak for some k or not.
2022-09-25