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In page Wave equation:

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For velocity impulse, s ( t , x ) = t δ D + 1 ( t , x ) {\displaystyle s(t,x)=\partial _{t}\delta ^{D+1}(t,x)} , so if we solve the Green function G {\displaystyle G} , the solution for this case is just t G {\displaystyle \partial _{t}G} .[citation needed]