Update src/7_tight_binding_model_sol.md

src/7_tight_binding_model_sol.md

@@ -38,4 +38,5 @@ pyplot.xlabel('$k$'); pyplot.ylabel('$v(k)$')
 pyplot.xticks([-pi/2, 0, pi/2], [r'$-\pi/2$', 0, r'$\pi/2$'])
 pyplot.yticks([0, 1], [0, r'$2\sqrt{\frac{\kappa}{m}}$'])
 pyplot.hlines([1], -pi/2, 0, linestyles='dashed')
+draw_classic_axes(ax)
 ```