diff --git a/src/11_nearly_free_electron_model_solutions.md - typo b/src/11_nearly_free_electron_model_solutions.md - typo
index 2656049fdfce0c5a7f36e15274ea9250f1fdf15f..036072a22207b85277e950dbf25f11d1f9a080a7 100644
--- a/src/11_nearly_free_electron_model_solutions.md - typo	
+++ b/src/11_nearly_free_electron_model_solutions.md - typo	
@@ -159,10 +159,10 @@ $$
 $$
 and
 $$
-\langle n-1|H_\overline{n}|n\rangle$ = \kappa \sum_{m \neq 0 }\int e^{\kappa|x-a|} e^{\kappa|x|}\delta(x-ma)  
+\langle n-1|H_\overline{n}|n\rangle$ = \kappa \sum_{m \neq 0 }\int e^{-\kappa|x-a|} \delta(x-ma)  e^{-\kappa|x|} =\kappa \sum_{m \neq 0 } e^{-\kappa a|m-1|} e^{-\kappa a |m|} =\kappa(e^{ka+e^{-ka}}) \sum_{m=1}^{m=\infty} e^{-2\kappa a m}
 $$
 
-In progress of being updated......
+Update in progress......
 
 \begin{equation}
 \varepsilon_0=\braket{n|\hat{H}|n}=\braket{n|\hat{K}|n}+\braket{n|\hat{V}(x)|n}