问题描述: tan70°cos10°(根号3xtan20°—1)x是乘号 1个回答 分类:数学 2014-10-23 问题解答: 我来补答 tan70×cos10×(√3tan20-1) =tan70×cos10×(tan60×tan20-1) =tan70×cos10×[(sin60×sin20/cos60×cos20)-1] =tan70×cos10×(sin60×sin20-cos60×cos20)/(cos60×cos20) =tan70×cos10×[-cos(60+20)]/(cos60 ×cos20) =-tan70×cos10×cos80/(cos60×cos20) =-tan70×cos10×sin10/(cos60×cos20) =-(sin70/cos70)×(1/2)×sin20/(cos60×cos20) =-(cos20/sin20)×sin20/(2cos60×cos20) =-1/(2cos60) =-1 展开全文阅读