计算:sin65+sin15sin10/sin25-cos15cos80(注:题目中的数字均为度数)
(sin65°+sin15°sin10°)/(sin25°-cos15°cos80°) =
(cos25°+sin15°sin10°)/(sin25°-cos15°sin10°) =
[cos(15°+10°)+sin15°sin10°]/[(sin(15°+10°)-cos15°sin10°)] =
[cos15cos10°-sin15°sin10°+sin15°sin10°]/[(sin15°cos10°+cos15sin10°-cos15°sin10°)] =
(cos15°cos10°)/(sin15°cos10°) =
cos15°/sin15° =
sin75°/cos75° =
tan75°=
tan(45°+30°)=
(tan45°+tan30°)=(1-tan45°*tan30°)=
(1+√3/3)/(1-√3/3)=
(3+√3)/(3-√3)=
(3+√3)^2/(9-3)=
(12+6√3)/6=
2+√3
。
。