The Johnson Circles

The Johnson circles are a triplet of congruent circles sharing a single point. Every triangle has exactly two Johnson triplets.
• The locators are the centers of the three circles. They form the Johnson triangle with circumcircle of the same radius.
• Johnson's theorem: the "reference triangle" with vertices the points of two-fold intersection has, surprisingly, a circumcircle of the same radius.
• The reference triangle is congruent to the Johnson triangle by homothety of factor .
• The anticomplementary circle with twice the radius touches the Johnson circles.
• The inscribed anticomplementary triangle is homothetic to the Johnson triangle with factor 2.
• The three locators and the origin are, surprisingly, such that each is the orthocenter of the three others.
• The homothetic center of the Johnson and reference triangle is the center of the nine-point circle of the reference triangle.


  • [Snapshot]
  • [Snapshot]
  • [Snapshot]
    • Share:

Embed Interactive Demonstration New!

Just copy and paste this snippet of JavaScript code into your website or blog to put the live Demonstration on your site. More details »

Files require Wolfram CDF Player or Mathematica.