11. Cardioids

Cardioids

Excel files: Cardioids (adjust n and k manually)      Cardioids (n as a linear function of k)      Cardioids-with Loops

A General Overview: A cardioid  can be obtained by connecting vertices of the polygon (1, 2), (2, 4), (3, 6) … (j, 2*j) for j = 1, …, n-1. Of course, many of the 2j second vertices will be larger than n in size … these points are simply the MOD n values of 2*j (MOD is the remainder upon division by n). For example, if n = 6 and j = 4 then the rule is to connect point 4 to 8, but 8 is the same as 2 because 2 = MOD(8, 6). Note that this is a second time to have drawn that particular line since (2, 4) was already drawn. Similarly, (5, 10) becomes (5, 4) because 4 = MOD(10, 6).

We can generalize the doubling rule to obtain multiple gathering points (or cusps) around the circle by changing the rule from (j, 2j) to (j, k*j). This will produce k-1 gathering points or cusps.

The cardioid images are created much like File 9, which creates general similar triangles using parallel lines, in that each of the lines is set independently from others, rather than as a single closed circuit as was the case in PART I. Interestingly, some of the relations between n and k produce images which are amenable to analysis using the counting rules discussed in PART II.

P15. Cardioids

1. Cardioid basics: 11.1a Cardioids are all about cusps
   • Take 2: 11.1b Lines in an Image
   • Take 3: 11.1c Three Special Cases
   • Take 4: 11.1d It helps to start at vertex 1
2. Symmetry 11.2a Vertical Symmetry
   • Take 2: 11.2b Rotational Symmetry
3. Measuring angles, Take 1: 11.3a Angles in Cardioids
   • Take 2: 11.3b Right Angles
4. Why the image appears curved 11.4 How the Image Curves
5. Adjacent interior angles 11.5a Adjacent Interior Angles
   • Implied exterior angles: 11.5b Implied Exterior Angles
6. Vertex Loops: 11.6a Vertex Loops
   • Take 2: 11.6b Identity and Paired Vertices
   • Take 3: 11.6c Ribbons and Strips
   • Take 4a: 11.6_4a Ribbons everywhere given n = 361, k = 18
     • MA. 4bi: 11.6_4bi Deconstructing Loops using Excel
       • MA. 4bii: Excel file: 11.6_4bii 361_18 Loop Explainer
7. The n = k single Circle Fan: 11.7a Vertices as Directions
   • Multiple Circle Fans: 11.7b Circle Fans show Remainders
8. MA. Searching for patterns using equations in Excel: 118a Examining n as a function of k, n(k)
   • Take 2: 11.8b Automating n(k) using the manual entry file
   • Take 3: 11.8c Using the n as a linear function of k file
9. MA. Deconstructing an image: 11.9 Deconstructing a Clock-face
10. Some interesting images
    • Mirrored Cardioids
    • Centered Regular Polygons and Stars
      • Counting Centered Regular Polygons and Stars

11. GLOSSARY

FOR USERS

Challenge Questions

11.Challenge Questions

11.Cardioid Counting Questions

11.Group Angle Project

11.Direction Labeling

11.Cusps and Circle Fans

11.Circle Fans and Cusps (no hints)

11. Ribbons and Loops

11. CRPS CQ A

11. CRPS CQ B

FOR INSTRUCTORS