(a)
Chapter 9, Problem 9(choose chapter or problem)
(a) Foranysolutionofthethree-dimensionalwaveequationwithinitial data vanishing outside some sphere, show that u(x, y,z,t)=0 for xed (x, y, z) and large enough t. (b) Provethatu(x, y,z,t)= O(t1)uniformlyast ;thatis,prove thatt u(x, y,z,t)isaboundedfunctionofx,y,z,andt.(Hint:Use Kirchhoffs formula.)
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