Find the general expression for all locations $(x\text{'}$s$)$ where the bending moment is zero

along a railway track that is subjected to a single wheel load. Note: Lecture notes

$($pages $35)$ have found only the first $x$ value for the location of zero bending moment,

but theoretically there are more locations as one moves further away from the load.

Location of Zero Moment $(x_1)$

$M=P(\frac{EI}{64k}{)}^{\frac{1}{4}}{e}^{-|x|}(cos|x|-sin|x|)$

$M=0$ when $(cos|x|-sin|x|)=0$longrightarrow$x_1=\frac{}{4}$