二阶抽象Cauchy方程与（C＿1，C＿2）存在唯一余弦族

Second Order Cauchy Problem and(C_1,C_2)一Existence and Uniqueness Cosine Families

本文首次引入了（Ｃ＿１，Ｃ＿２）存在唯一余弦族的概念，并初步探讨了（Ｃ＿ｉ。

in this paper the concept of(C_1,C_2)existence and uniqueness cosine families isintroduced firstly. The basic properties of(C_1.C_2)一cosine families and the relation betweenit and Second order ACP are discussed.