What is a z-Score, and Why?
Last time we looked at some questions about drawing or interpreting the normal curve (graph of the normal distribution). Let’s back up and consider what it actually is. In particular, we’ll see what the “z-score” means.
What Does the Normal Curve Really Look Like?
We’ll look here at a recent question, and another from a year ago that it reminded me of. I see a lot of inaccurate sketches of the normal distribution, usually from statistics students (in which case accuracy isn’t really important, but can show that you know what you’re talking about), and sometimes elsewhere.
Names of Small Numbers: One to Twenty
Having looked at words for large numbers, let’s turn to the less-asked, but still interesting, question of where our words (in English) for ordinary little numbers come from. We’ll look at the origins of one, two, three, then eleven, twelve, thirteen, and then first, second, third.
Names of Large Numbers: Vigintillion and Beyond
Last time we looked at names of anniversaries (like “semiquincentennial” for the 250th), and other words based on Latin numbers (like “septuplets” for 7 babies). Let’s back up and look at the names in English for large numbers themselves, like million, trillion, and vigintillion. We’ll work up to the big ones!
What is a Semiquincentennial?
This is the 250th anniversary of the United States, and as a result we’ve heard the term “semiquincentennial” a lot. (Well, a lot more than usual.) That reminded me of several past questions about such terms, so we’ll take a look at them now, starting (after a quick introduction) with one asked 25 years ago …
Proving √2 is Irrational: Minding the Gaps
Recently, a teacher in Bangladesh asked us how to answer students’ common questions about his version of the proof that the square root of 2 is an irrational number. Some are questions about apparent gaps in the proof itself, others about how one would decide what to do in writing the proof. We’ll then compare …
Hyperbolic and Circular Functions and Complex Numbers
Last time we looked at what hyperbolic functions are, as a parallel world to trigonometric (circular) functions. But there’s another parallel: Each is related to the other through complex numbers. We’ll look at several questions that open the door to this relationship, finding how to calculate trig functions of complex numbers, and then delving into …
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What Are Hyperbolic Functions?
Hyperbolic functions are functions that form a sort of parallel universe to the trigonometric functions. They are typically introduced as an aside while teaching calculus – because they happen to be useful there, and also because they can’t really be understood without calculus. As a result, we can easily misunderstand them, forget about them, and …
Solving Polynomial and Rational Inequalities
A recent question asked about quadratic inequalities; we’ve touched on that in Domain, Range, and Quadratic Inequalities, but here we’ll introduce three basic approaches. We’ll follow that with old questions about polynomial inequalities (mostly quadratic) and rational inequalities (fractions), expanding on the basic methods.
Exploring Descartes’ Rule of Signs
We’ve discussed the Rational Root Theorem in the past, but not a theorem that is often taught along with it, namely Descartes’ Rule of Signs, which predicts the numbers of positive and negative zeros (roots) of a polynomial. Both are ascribed to Rene Descartes; both are often taught without proof. Here we’ll introduce the theorem, …