HOMEWORK: (click here for comments / solutions to the HW)
Please spend at least 1 if not 2 hours a night reading the material/looking at the proofs/making sure you can do the algebra. Below is a tentative reading list and homework assignments. It is subject to slight changes depending on the amount of material covered each week. I strongly encourage you to skim the reading before class, so you are familiar with the definitions, concepts, and the statements of the material we'll cover that day.
(1) Let N be a large integer. How should we divide N into positive integers ai such that the product of the ai is as large as possible. Redo the problem when N and the ai need not be integers.
(2) What is wrong with the following argument (from Mathematical Fallacies, Flaws, and Flimflam - by Edward Barbeau): There is no point on the parabola 16y = x2 closest to (0,5). This is because the distance-squared from (0,5) to a point (x,y) on the parabola is x2 + (y-5)2. As 16y = x2 the distance-squared is f(y) = 16y + (y-5)2. As f'(y) = 2y+6, there is only one critical point, at y = -3; however, there is no x such that (x,-3) is on the parabola. Thus there is no shortest distance!
(3) Without using any computer, calculator or computing by brute force, determine which is larger: eπ or πe. (In other words, find out which is larger without actually determining the values of eπ or πe). If you're interested in formulas for π, see also my paper A probabilistic proof of Wallis' formula for π, which appeared in the American Mathematical Monthly (there are a lot of good articles in this magazine, many of which are accessible to freshmen).
Future problems: Monte Carlo Exercises: (1) write a program to estimate the
area of a quarter of the unit
circle; (2) let f be a probability distribution with finite mean and variance.
Prove there exist a and b such that (i) g(x) = f(x+a) has mean zero and the
same standard deviation as f, and (ii)
h(x) = g(bx) = f(b(x+a)) has mean 0 and variance 1. This result is important
because it normalizes different distributions and makes them more easily
comparable. For a nice distribution, you don't really start to see the shape
until the third or fourth moment (in general). This feature is responsible for
some incredibly universality of behavior (see the Central Limit Theorem in
Math 162). Page 375: #3, #8. Page 390: #4, #7, #10, #15, #18, #31.
Extra Credit: (1: 1 point) Prove Newton's result that you may
assume all the mass of a sphere of radius 1 with uniform density is
concentrated at the center. As the book proves this using potentials,
you must prove this by direct integration of the force. (2: 2 points) Assume the force of gravity is given
by (GMm/rn-1) er in n-dimensional space.
Here er is the unit vector in the r-direction. Thus the
magnitude of the force is GMm/rn-1 and it is radial. Prove or disprove: we
may assume all the mass of a sphere of radius 1 with uniform density is
concentrated at the center (ie, the force this exerts is the same as the force
of the sphere).