| 摘 要： | In this paper, we can struct the elementary solution of ultra-hyperbolic equation with constant coeffi-cient by the characteristic conoid. By using the fundmental formula and the elementary solution analyse theform of its solution and give an explicit formula of the solution at the vertex of the characteristic conoid.Finally, we discuss the necessary condition for the initial value problem. This method can be used in the ul-tra-hyperbolic equation with the problem varible coefficient,1 The Elementary SolutionConsider equation,
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