i (mostly) agree.  i think thinking about a fraction of a full circle is the easiest way to work with trig.  having said that, the mental overload on your average high school student flipping between pi and tau is too much.  my personal compromise is to never cancel out the &#x27;2&#x27; and always work with 2pi.  it makes some equations look a bit odd from the textbook but whacks me in the forehead to remember to think about circles...