Math 617 Final Examination, December 16, 2003, Exams of Mathematics

The final examination for math 617, theory of functions of a complex variable i, taught by dr. Boas at [university name] in 2003. The examination consists of 16 problems that cover various topics in complex analysis, such as holomorphic functions, simple closed curves, residues, and linear fractional transformations. Students are expected to provide concrete examples or prove that no example exists for each problem.

Typology: Exams

Pre 2010

Uploaded on 02/10/2009

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Math 617 Final Examination December 16, 2003
Instructions In each item, either give a concrete example satisfying the
conditions or prove that no example exists (whichever is appropriate). Work
as many of the 16 items as you wish.
Your score for ncorrect items is 10min(n, 8) + 5 max(n8,0); that is,
your first 8 correct items count 10 points each, and additional correct items
count 5 points each. (More than 12 correct items will give you extra credit:
namely, a score greater than 100.)
1. A non-empty open set Uand a holomorphic function fon Usuch that
there does not exist a holomorphic function gon Uwith the property
that the derivative g0=f.
2. A non-empty open set U, a holomorphic function fon U, and a simple
closed curve γin Usuch that Rγf(z)dz =2.
3. A holomorphic function fon the unit disc {zC:|z|<1}such that
the nth derivative f(n)(0) = (n!)2for every positive integer n.
4. A non-polynomial entire function with exactly one zero.
5. A holomorphic function fon the disc {zC:|z|<2}such that
f(1/n)=(1)n/n for every positive integer n.
6. A holomorphic function fon the punctured disc {zC:0<|z|<2}
such that R|z|=1 f(z)dz = 0, and fhas an essential singularity at the
origin.
7. A rational function fhaving a pole at 0 such that the residue of fat 0
equals 2 and the residue of the derivative f0at 0 equals 1.
8. A positive real number asuch that Z
−∞
1
x4+a4dx =1.
Theory of Functions of a Complex Variable I Dr. Boas
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Math 617 Final Examination December 16, 2003

Instructions In each item, either give a concrete example satisfying the conditions or prove that no example exists (whichever is appropriate). Work as many of the 16 items as you wish. Your score for n correct items is 10 min(n, 8) + 5 max(n − 8 , 0); that is, your first 8 correct items count 10 points each, and additional correct items count 5 points each. (More than 12 correct items will give you extra credit: namely, a score greater than 100.)

  1. A non-empty open set U and a holomorphic function f on U such that there does not exist a holomorphic function g on U with the property that the derivative g′^ = f.
  2. A non-empty open set U , a holomorphic function f on U , and a simple closed curve γ in U such that

γ f^ (z)^ dz^ =^

  1. A holomorphic function f on the unit disc { z ∈ C : |z| < 1 } such that the nth derivative f (n)(0) = (n!)^2 for every positive integer n.
  2. A non-polynomial entire function with exactly one zero.
  3. A holomorphic function f on the disc { z ∈ C : |z| < 2 } such that f (1/n) = (−1)n/n for every positive integer n.
  4. A holomorphic function f on the punctured disc { z ∈ C : 0 < |z| < 2 } such that

|z|=1 f^ (z)^ dz^ = 0, and^ f^ has an essential singularity at the origin.

  1. A rational function f having a pole at 0 such that the residue of f at 0 equals 2 and the residue of the derivative f ′^ at 0 equals 1.
  2. A positive real number a such that

−∞

x^4 + a^4

dx = 1.

Theory of Functions of a Complex Variable I Dr. Boas

Math 617 Final Examination December 16, 2003

  1. A holomorphic function (not necessarily one-to-one) that maps the unit disc { z ∈ C : |z| < 1 } onto the punctured disc { z ∈ C : 0 < |z| < 1 }.
  2. A continuous function f on the closed disc { z ∈ C : |z| ≤ 1 } that is holomorphic in the open disc, has 617 simple zeroes in the open disc, and satisfies the inequality |f (z)| ≤ 1 when |z| ≤ 1.
  3. A continuous function on the upper half-plane { z ∈ C : Im z ≥ 0 } that is holomorphic in the open half-plane and that satisfies the property sup{ |f (z)| : Im z > 0 } 6 = sup{ |f (z)| : Im z = 0 }.
  4. A linear fractional transformation (M¨obius transformation) f such that f (1) = 1, f (2) = 4, f (3) = 9, and f (4) = 16.
  5. A holomorphic function mapping the unit disc { z ∈ C : |z| < 1 } into itself such that f (1/2) = − 1 /2, and the derivative f ′(1/2) = 1.
  6. A family of entire functions such that the image of each function is contained in the punctured plane C \ { 0 }, and the family is not a normal family.
  7. A continuous, real-valued function on the plane C whose restriction to the upper half-plane { z ∈ C : Im z > 0 } is harmonic and whose restriction to the lower half-plane { z ∈ C : Im z < 0 } is harmonic, but which is not a harmonic function on all of C.
  8. A continuous, real-valued function u on the closed unit disc { z ∈ C : |z| ≤ 1 }, harmonic in the open disc, such that u(1/2) = 3/4, and |u(z)| ≤ 1 on the boundary of the disc.

Theory of Functions of a Complex Variable I Dr. Boas