Connecting the Tangent Function to Cardinality: A Method for Introducing Set Theory to High School Students

High school students often ask questions about the nature of infinity. When contemplating what the "largest number" is, or discussing the speed of light, students bring their own ideas about infinity and asymptotes into the conversation. These are popular ideas, but formal ideas about the nature of mathematical sets, or "set theory," are generally unknown to high school students. The authors propose a method for introducing basic ideas in set theory to high school trigonometry students by connecting prior knowledge of the tangent function and the unit circle to Georg Cantor's ideas about infinity. By doing so, high school teachers have an opportunity to inspire their students with rich mathematics.