For part (a), the function is $D(x, t)=A \ln (x+v t)$.
The first derivative with respect to x is $\frac{\partial D}{\partial x} = \frac{A}{x+vt}$.
The second derivative with respect to x is $\frac{\partial^2 D}{\partial x^2} = -\frac{A}{(x+vt)^2}$.
The
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