(sin10度+sin20)/(cos10+cos20)
问题描述:
(sin10度+sin20)/(cos10+cos20)
答
把10°变为15°-5°,20°=15°+5°;展开合并得:
(sin10°+sin20°)/(cos10°+cos20°)=2sin15°cos5°/2cos15°cos5°=2sin^215°/2sin15°cos15°
=(1-cos30°)/sin30°=2-根号3