2.2 Solved by factoring into two transport equations

  2.2.1 \(u_{xx} + u_{xt} - 6 u_{tt} = 0\)
  2.2.2 \(u_{xx} - u_{xt} - 12 u_{tt} = 0\)
  2.2.3 \(u_{xx} - 3 u_{xt} - 4 u_{tt} = 0\)
  2.2.4 \(u_{tt} - 2 u_{xt} - 3 u_{xx} = 0\) with \(u(0,x)=x^2, u_t(x,0)=e^x\)

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