For a more extensive discussion, see N. Gregory Mankiw, Macroeconomics, Fourth Edition (New York, N.Y.: Worth Publishers, 2000), pp. 90-97; or Olivier Blanchard, Macroeconomics, Second Edition (Upper Saddle River, N.J.: Prentice Hall, 2000), pp. 214-220.
There is a more extensive discussion in Macroeconomics, Fourth Edition.