  The geometry of 2D Minkowski spacetime $\mathbb{R}^{1,1}$ (or Minkowski
plane) is similar but fundamentally different from the more familiar Euclidean
plane geometry. This note gives an elementary discussion on some basic
properties of a triangle on the Minkowski plane. In particular, we show that
the theorem of Feuerbach also holds and a use of the incenter/excenters is
pointed out.
