| Line 9: | Line 9: | ||
Parametrize the circular part of the boundary via | Parametrize the circular part of the boundary via | ||
| − | <math> | + | <math>C_R:\quad z(t)=Re^{it}, 0<t<\pi/4.</math> |
You need to show that | You need to show that | ||
| Line 19: | Line 19: | ||
<math>|I_R|\le\int_0^{\pi/4} Re^{-R^2\cos(2t)}\,dt</math> | <math>|I_R|\le\int_0^{\pi/4} Re^{-R^2\cos(2t)}\,dt</math> | ||
| − | and use freshman calculus ideas to show that this integral tends to zero. (Don't hit it with the big stick, the Lebesgue Dominated Convergence Theorem.) | + | and use freshman calculus ideas to show that this integral tends to zero. (Don't hit it with the big stick, the Lebesgue Dominated Convergence Theorem.) Hint: Draw the graph of cos_2t on the interval and realize that the line connecting the endpoints is under the graph. Compare the integral with what you would get by replacing cos_2t by the simple linear function underneath it. |
Revision as of 10:44, 9 February 2011
Homework 4 discussion area
Problem 7 hint:
$ e^{\pm f(z)} $
Problem 10 hint:
Parametrize the circular part of the boundary via
$ C_R:\quad z(t)=Re^{it}, 0<t<\pi/4. $
You need to show that
$ I_R := \int_{C_R}e^{-z^2}\ dz\to 0 $
as R goes to infinity. You won't be able to use the standard estimate to do this. Write out the definition of the integral to find that
$ |I_R|\le\int_0^{\pi/4} Re^{-R^2\cos(2t)}\,dt $
and use freshman calculus ideas to show that this integral tends to zero. (Don't hit it with the big stick, the Lebesgue Dominated Convergence Theorem.) Hint: Draw the graph of cos_2t on the interval and realize that the line connecting the endpoints is under the graph. Compare the integral with what you would get by replacing cos_2t by the simple linear function underneath it.
