How can I obtain the common tangent of two curves within

*To*: mathgroup at smc.vnet.net*Subject*: [mg114904] How can I obtain the common tangent of two curves within*From*: Hongyi Zhao <hongyi.zhao at gmail.com>*Date*: Wed, 22 Dec 2010 02:35:41 -0500 (EST)

Dear all, I've two curves corresponding to two functions, say, y=f_1(x), and y=f_2(x). Now, I want to obtain the common tangent of these two curves within mathematica? What code or commands I should use for this purpose? Thanks in advance. Best regards.