diff --git a/src/7_tight_binding_model_solutions.md b/src/7_tight_binding_model_solutions.md
index ac2c70c37aaa353c41c0e15d8fa0167e4202b652..afa6987c0973fea6f32d34e0e893c168641c0cb7 100644
--- a/src/7_tight_binding_model_solutions.md
+++ b/src/7_tight_binding_model_solutions.md
@@ -29,7 +29,7 @@ Hint: What kind of particles obey Bose-Einstein statistics? What kind of 'partic
 
 ### Subquestion 2
 
-Group velocity is given as $v=\hbar^{-1}\frac{\partial E}{\partial k}$ with $E=\hbar\omega$ and $g(\omega) = \frac{dN}{d\omega} = \frac{dN}{dk}\frac{dk}{d\omega}$. So we find: $$ v(k) = a\sqrt{\frac{\kappa}{m}}\cos(\frac{ka}{2})\frac{|k|}{k}$$ $$ g(\omega) = \frac{L}{\pi}\frac{d}{d\omega} \bigg [\frac{2}{a}\sin^{-1}\bigg(\sqrt{\frac{m}{\kappa}}\frac{\omega}{2} \bigg) \bigg ] \\ = \frac{L}{\pi a} \frac{1}{\sqrt{\frac{4\kappa}{m}-\omega^2}}$$
+Group velocity is given as $v=\hbar^{-1}\frac{\partial E}{\partial k}$ with $E=\hbar\omega$ and $g(\omega) = \frac{dN}{d\omega} = \frac{dN}{dk}\frac{dk}{d\omega}$. So we find: $$ v(k) = a\sqrt{\frac{\kappa}{m}}\cos(\frac{ka}{2})\frac{|k|}{k}$$ $$ g(\omega) = \frac{2L}{\pi}\frac{d}{d\omega} \bigg [\frac{2}{a}\sin^{-1}\bigg(\sqrt{\frac{m}{\kappa}}\frac{\omega}{2} \bigg) \bigg ] \\ = \frac{L}{\pi a} \frac{1}{\sqrt{\frac{4\kappa}{m}-\omega^2}}$$
 
 ### Subquestion 3