Cos(a+π/3)+tg(2a+π/3), a= -π/6
Cos(-pi/6+pi/3) + tg(0) = cos(-pi/6)cos(pi/3) + sin(-pi/6)sin(pi/3)= = √3/2 * 1/2 + (-1/2)*√3/2 + 0 = √3/4 - √3/4 + 0 = 0.