求值(cot20°-根号3)(cos5°+sin5°)(cos5°-sin5°),要详程

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求值(cot20°-根号3)(cos5°+sin5°)(cos5°-sin5°),要详程

求值(cot20°-根号3)(cos5°+sin5°)(cos5°-sin5°),要详程
求值(cot20°-根号3)(cos5°+sin5°)(cos5°-sin5°),要详程

求值(cot20°-根号3)(cos5°+sin5°)(cos5°-sin5°),要详程
(cot20°-根号3)(cos5°+sin5°)(cos5°-sin5°)
=(cot20°-根号3).(cos5°^2-sin5°^2)
=(cot20°-根号3).cos10°
=(cos20`/sin20`-根号3).cos10°
==(cos20`/2sin10`cos10`-根号3).cos10°
=cos20`/2sin10`-根号3cos10`
=(cos20°-2根号3cos10sin10)/2sin10`
==(cos20°-根号3sin20)/2sin10
=cos100`/sin10`
=-sin10`/sin10`=-1