sin(-23π/6)=sin(-4π+π/6)=sinπ/6=1/2.
或,原式=sin[-(4π-π/6)].
=-sin(4π-π/6)
=-(-(1/2)
=1/2.
补：
由韦达定理得：
tana+1/tana=k,(1)
tana*1/tana=k^2-3(2)