先用三倍角公式化解!sin(3a)=3sina-4sin^3 a cos3a =4cos^3 a-3cosa 代入可得,(3sin10-4sin^3 10)/sin10-(4cos^3 10-3sin10)/cos10=(3-4sin^2 10)-(4cos^2 10-3)=3+3-4(sin^2 10+cos^2 10)=2