原式=ln[(1/sinu)-(cosu/sinu)]+cosu=ln[(1-cosu)/sinu]+cosu|<π/6,π/2>={ln[(1-0)/1]+0}-{ln[(1-√3/2)/(1/2])+(√3/2)}=0-[ln(2-√3)+(√3/2)]=-[ln(2-√3)+(√3/2)]
