Hi,

I don't know how to find the exact value of arctan (-2). By graphing, I know that it's approximately -1.107 (tan -1.107 = -2), but is there a simpler exact version of that, like 2pi/3 or 1/sqrt(3)? I can't find it in any trig chart and I don't know of any way to derive it from the known values in a trig chart.