(1)1-tan15/(1+tan15) (2)(1-根号3tan75)/(根号3+tan75

(1-tan15)/(1+tan15)
=(1-sin15/cos15)/(1+sin15/cos15)
=(cos15-sin15)/(cos15+sin15)
利用这个结果
http://zhidao.baidu.com/question/80118882.html
=-√3/3

(1-√3tan75)/(√3+tan75)
=(1-tan60tan75)/(tan60+tan75)
=1/[(tan60+tan75)(1-tan60tan75)]
=1/tan(60+75)
=1/tan135
=1/(-1)
=-1