# Origins of the Coordinate Plane

One of the legends of math relates to the invention of the coordinate plane system. The legend states that Descartes was inspired to invent this system after watching a fly move around on the ceiling over his bed. This post tells the story and points out its relevance for modern math teachers.

# How to tell if a Number is Divisible by 8

How to tell if 8 divides into a number. There is a simple test for this. This post explains this.

# Recent insight on the GCF (and GPGCF)

Two factors limit the size of the GCF for any two numbers. Those factors are: 1) the difference between the two numbers, and 2) the size of the smaller of the two numbers. Whichever of these two factors is smaller is the Greatest Possible Greatest Common Factor, also known as the GPGCF.

# Not all variables are created equal

Variables do not all serve the same purpose. Making this clear helps students more deeply understand algebraic equations, such as the equation for a line. This post shows how to understand the two kinds of variables in the slope-intercept form of a linear equation.

# Finding domain and range — with color!

Finding the domain and range of functions confuses many students. Using color to code the domain and range separately helps students distinguish domain and range, and thereby helps them find the domain and range for continuous functions.

# Common Algebra Mistake: Interpreting Negative Signs in Front of Parentheses

Tricky area of algebra: negative signs in front of parentheses. This explains how we can help students relate the concept to everyday life, and thereby grasp it so they remember it!