One Team, Two Teams, My Team, Your Team
(A new question of the week) Counting ways to select teams can be simple, or quite complex. Here we’ll look at a few tricky examples.
Finding a Symmetric Polynomial Given Others
A recent question (whose asker refused to cooperate by showing work, so that we were unable to help) reminded me that we haven’t yet shown a similar kind of problem that can be quite interesting: problems where we are given the value of one or several expressions in several variables, and are asked for the …
A Challenging Homogeneous Second-Order Recurrence
(An archive question of the week) In preparing the last couple posts, on recurrence relations, I ran across an answer to a much harder question, that illustrates what it can take to solve one that doesn’t fit the convenient forms. It’s linear, but the coefficients are not constant as they have been in all our …
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Introduction to Non-homogeneous Recurrences
Last week we looked at Ask Dr. Math questions about homogeneous linear recurrences; this time we’ll see some on simple (first-order) non-homogeneous recurrences, which will bring us back to the topic two weeks ago, when we looked at the examples of this type that a student had the most trouble with. This will be an …
Homogeneous Linear Recurrence Relations
Last week we looked at a recent question about recurrence relations, and I realized it needs a companion article to introduce these ideas. So here we will look at some answers from Ask Dr. Math about the simpler case, including general methods, why they work, and applications.
Non-homogeneous Recurrence Relations
(A new question of the week) A recent question asked us to find errors in solving recurrence relations by the method of undetermined coefficients. We’ll see several things that can go wrong, and correct some misunderstandings.
Using the Angle Sum and Difference Identities
Here is a short discussion of a common type of problem in trigonometry classes: finding a trig function of the sum or difference of two angles, given minimal information about them.
Advanced Logarithm Problems
(A new question of the week) Here is an interesting collection of problems involving logarithms with different bases, which require some unique thinking. And after we’d worked out a good strategy, another problem arose at a whole new level.
Fine Points on Polygons and Polyhedra
Last time, looking at degenerate polygons, I mentioned some other issues pertaining to the definition of a polygon. Let’s take the opportunity to look at them. This post supplements what was said previously in What is a Polyhedron … Really?
Degenerate Polygons
We’ve been looking at degenerate figures, starting with the most interesting case, degenerate conic sections. But other things can also be degenerate, so we should take a look at some of these, which perhaps arise even more often. We’ll examine triangles that aren’t triangles, rectangles that aren’t rectangles, and bigger polygons – or smaller polygons! …