对１９９４年高考２２题一种证法的推敲汤先键（兰州市万里中学７３００７０）题目已知函数ｆ（ｘ）＝ｔｇｘ，若ｘ１，且ｘ１≠ｘ２，证明［１］、［２］、［３］等文给出了“凸函数”证法：证明如图，ｆ（ｘ）＝ｔｇｘ，是下凸函数，在正切曲线上任取两点Ｐ１（ｘ１，ｔ... Question of a certificate method for the 1994 college entrance examination in 22 questions Tang Xianjian (Lanzhou Wanli Middle School 730070) Topic-known function f(x)=tgx, if x1, and x1≠x2, prove [1], [2], [3 ] and other papers give the “convex function” proof method: Prove that, f(x) = tgx, is a convex function, take two points P1 (x1, t...