15°=π/12 75°=5π/12=π/2-π/12cos(π/2-π/12)=sinπ/12
(√3cos15°+sin15°)cos/75°=(√3cosπ/12+sinπ/12)/cos(π/2-π/12)=√3cotπ/12
cotπ/12=2+√3
原式=2√3+3