Qualifying Exam in Complex Variables

Fall 1997

  1. Let exam_images/complex-fall971.jpg be holomorphic on some open set exam_images/complex-fall972.jpg of exam_images/complex-fall973.jpg . Let exam_images/complex-fall974.jpg such that exam_images/complex-fall975.jpg . Show that if exam_images/complex-fall976.jpg is a circle of center exam_images/complex-fall977.jpg and small enough radius then:

    exam_images/complex-fall978.jpg



  2. Suppose that exam_images/complex-fall979.jpg is a continuous function on exam_images/complex-fall9710.jpg such that, for each exam_images/complex-fall9711.jpg , the function exam_images/complex-fall9712.jpg is holomorphic. Show that the following function is holomorphic:

    exam_images/complex-fall9713.jpg



  3. Show that if exam_images/complex-fall9714.jpg then

    exam_images/complex-fall9715.jpg



  4. Let exam_images/complex-fall9716.jpg be holomorphic on some open set exam_images/complex-fall9717.jpg containing the closed disk exam_images/complex-fall9718.jpg of center 0 and radius exam_images/complex-fall9719.jpg . Let exam_images/complex-fall9720.jpg be the zeroes of exam_images/complex-fall9721.jpg in the open disc, each zero being repeated according to its multiplicity. Prove that

    exam_images/complex-fall9722.jpg

    Hint: apply the maximum principle to the function

    exam_images/complex-fall9723.jpg



  5. Let exam_images/complex-fall9724.jpg be the set of complex numbers exam_images/complex-fall9725.jpg with exam_images/complex-fall9726.jpg real and exam_images/complex-fall9727.jpg . Suppose that exam_images/complex-fall9728.jpg is holomorphic on exam_images/complex-fall9729.jpg and such that exam_images/complex-fall9730.jpg for all exam_images/complex-fall9731.jpg . Show that exam_images/complex-fall9732.jpg has an expansion of the form

    exam_images/complex-fall9733.jpg

    where

    exam_images/complex-fall9734.jpg

    for any exam_images/complex-fall9735.jpg . Hint: regard exam_images/complex-fall9736.jpg as a function of exam_images/complex-fall9737.jpg . Now suppose that there is exam_images/complex-fall9738.jpg such that for exam_images/complex-fall9739.jpg the function exam_images/complex-fall9740.jpg is uniformly bounded. Show that exam_images/complex-fall9741.jpg for exam_images/complex-fall9742.jpg .

  6. Define the Zeta function exam_images/complex-fall9743.jpg and the Bernouilli numbers exam_images/complex-fall9744.jpg by

    exam_images/complex-fall9745.jpg

    Thus exam_images/complex-fall9746.jpg , exam_images/complex-fall9747.jpg and exam_images/complex-fall9748.jpg for exam_images/complex-fall9749.jpg . Express the coefficients of the power series expansion (at exam_images/complex-fall9750.jpg ) of the function

    exam_images/complex-fall9751.jpg

    in terms of the Bernouilli numbers. On the other hand, recall the formula

    exam_images/complex-fall9752.jpg

    Use the logarithmic derivative of this identity to obtain another power series expansion for exam_images/complex-fall9753.jpg and conclude that

    exam_images/complex-fall9754.jpg


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