7.4

E^{'} = (\frac{h^{2}}{8 L^{2} m}) (n_{x}^{2} + n_{y}^{2} + n_{z}^{2})

${E' = \left (\frac {h^2} {8L^2m} \right) (n^2_x + n^2_y + n^2_z)}$

Error