Wave Equation - Initial Value Problem

Question

Given $$ u_{tt}−\Deltau = 0, \ \ for \ \ t≥ 0, \ x∈ \mathbb{R^3} $$ With initial conditions $$ u(x, 0) = cos|x| $$ $$ u_t(x, 0) = 1 $$ Find $u(0, t)$ for all times $t>0$ $$$$ Perhaps here it is possible to somehow use D'Alambert's formula by reducing the system to radial coordinates using $r$ instead of $(x_1,x_2,x_3)$ ? Thank you for your help.

Answer 1

I figured it out. Use Kirchhoff Formula