2 cos(pi/6 t- 2pi/3) = 0 cos(A-B)=cos A cos B + sin A sin B 2 ( Cos(tpi/6)cos(2pi/3) +sin(tpi/6)sin(2pi/3)) 2 ( cos(tpi/6)*-0.5 + sin(tpi/6)*root3 /2 ) root3 sin(tpi/6) - cos(tpi/6) = 0 root3 sin(tpi/6) = cos(tpi/6) root3 = cos(tpi/6) / sin(tpi/6) root3 = cot (tpi/6) root3 = tan (6/tpi) Arctan (root3) = 6/tpi pi / 3 = 6/tpi t pi^2 = 18 t = 18/pi^2 is aprox 1.82 I enjoyed working through this one!