原式=tan(13π/3) - sin(5π/2) + cos(23π/6)
=tan(4π + π/3) - sin(2π + π/2) + cos(4π - π/6)
=tan(π/3) - sin(π/2) + cos(π/6)
=√3 - 1 + √3/2
=(3√3)/2 - 1