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Complex Line Integrals I

Part 1: The definition of the complex line integral

Let f be a continuous complex-valued function of a complex variable, and let C be a smooth curve in the complex plane parametrized by

Z(t) = x(t) + i y(t) for t varying between a and b.

Then the complex line integral of f over C is given by


Note that the "smooth" condition guarantees that Z' is continuous and, hence, that the integral exists.

We will consider line integrals of the following functions

over a varierty of different curves.

  1. Calculate the line integral of the square function, f2, over the curve C1, the parabola y = x2 from 0 to 1 + i, using the parametric representation

    Z(t) = t + t2i    for t between 0 and 1.

    Repeat the calculation for the parametric representation

    Z(t) = t 2+ t4i    for t between 0 and 1.

    Now repeat the calculation using your own parametric representation for C1.

  2. Repeat Step 1 for the function f4.

  3. Summarize your calculations in Steps 1 and 2.

  4. Next we consider integrating our functions f2 and f4 over a number of different curves that connect 0 to 1 + i. Use the given parametric representations for the curves C2 and C3 to calculate the integrals

    where C2 and C3 are the curves displayed below. Record your results. What do you observe about the values of the integrals?

  5. Let C4 be the top half of the unit circle traced out from 1 to -1, and let C5 be the bottom half of the unit circle traced out from 1 to -1.

    Calculate the integrals of all four functions over each of the two curves and record your results. (Check to make sure that your parametric representations trace out the curves in the correct directions. Also check the bounds on your parametric intervals.)

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