Midterm Exam 2 - Complex Variables | MATH 421, Exams of Mathematics

Material Type: Exam; Professor: Markman; Class: Complex Variables; Subject: Mathematics; University: University of Massachusetts - Amherst; Term: Fall 2002;

Typology: Exams

Pre 2010

Uploaded on 08/19/2009

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Math 421 Midterm 2 Fall 2002
Name:
Solve the first 5 problems and only one out of problems 6 and 7. (If you solve both
6 and 7, then I will not grade 7).
1. (20 points)
Compute the contour integral
ZC
e¯zdz,
where Cis the boundary of the rectangle with vertices at the points 0, 2, 2 + i,
and i, oriented counterclockwise. Caution: the exponent of the integrand is the
complex conjugate ¯zof z.
pf3
pf4
pf5
pf8

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Math 421 Midterm 2 Fall 2002

Name:

Solve the first 5 problems and only one out of problems 6 and 7. (If you solve both 6 and 7, then I will not grade 7).

  1. (20 points) Compute the contour integral (^) ∫

C

ez¯^ dz,

where C is the boundary of the rectangle with vertices at the points 0, 2, 2 + i, and i, oriented counterclockwise. Caution: the exponent of the integrand is the complex conjugate z¯ of z.

  1. (18 points) Let C be the circle of radius 5 centered at the origin and transversed counterclockwise. Compute (^) ∫

C

ez z^2 + 1

dz.

  1. (16 points) Prove the equality ∣∣ ∣ ∣

C

z + 1 z − 1

dz

∣ ≤^3 π,

where C is the semi-circle, given by the parametrization z(t) = 2eit, 0 ≤ t ≤ π.

  1. (16 points) Let C 1 be the curve, consisting of the piece of the graph of y = sin(x), given by the parametrization

z(x) = (x + i sin(x)), 0 ≤ x ≤ 2 π.

Let C 2 be the piece of the graph of y = − sin(x), given by the parametrization

z(x) = (x − i sin(x)), 0 ≤ x ≤ 2 π.

Compute the difference (^) ∫

C 1

dz z − π 2

C 2

dz z − π 2

  1. (12 points) a) (4 points) Let f (z) and g(z) be entire functions, and set P (z) := f (z)g(z). Prove the equality

P ′(z) P (z)

f ′(z) f (z)

g′(z) g(z)

b) (8 points) Let P (z) be a polynomial of degree n. Let CR the circle of radius R > 0, centered at the origin, transversed counterclockwise. Prove, the equality ∫

CR

P ′(z) P (z)

dz = 2 nπi,

provided R is sufficiently large. Hint: Do the case n = 1 first.