(sin10度+sin20)/(cos10+cos20)

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(sin10度+sin20)/(cos10+cos20)
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(sin10度+sin20)/(cos10+cos20)
(sin10度+sin20)/(cos10+cos20)

(sin10度+sin20)/(cos10+cos20)
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

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