行文之前,笔者先交代两个概念,一个是两曲线的公切线,另一个是两曲线相切.本文约定:若存在某一条直线l,既与曲线C,相切,同时又与曲线C_2相切,则称该直线l为两曲线C_1与C_2的公切线.另一个概念是两曲线相切,目前,在高中阶段,并没有明确提出两曲线相切这一概念,然而两条曲线相切这一情形在日常教学中经常遇到,这里为了方便起见,特给出高等数学中的定义:若两条曲 Before writing, I first explain two concepts, one is the common tangent of the two curves, the other is the tangent of the two curves.This paper agreed: If there is a straight line l, both with the curve C, tangent, and at the same time with the curve C_2 phase Cut, then said the straight line l is the common tangent of the two curves C_1 and C_2 Another concept is that the two curves tangent, at present, in the high school stage, and did not explicitly put forward the concept of tangency of the two curves, but the two tangent tangent This situation is often encountered in daily teaching, here for convenience, especially given the definition of advanced mathematics: If the two songs