fix misformatted equations

docs/4_sommerfeld_model_solutions.md

@@ -77,8 +77,8 @@ See hint of the question
 
 
 \begin{gather}
-g(\varepsilon)\textrm{d} \varepsilon = 2_s g(k)  \textrm{d} k
-g(\varepsilon)=2_sg(k(\varepsilon))\frac{\textrm{d} k}{\textrm{d} \varepsilon}
+g(\varepsilon)\textrm{d} \varepsilon = 2_s g(k)  \textrm{d} k\\
+g(\varepsilon)=2_sg(k(\varepsilon))\frac{\textrm{d} k}{\textrm{d} \varepsilon}\\
 g(\varepsilon) = \frac{2_s}{\Gamma(\frac{n}{2})}\left(\frac{L}{\hbar}\sqrt{\frac{m}{2\pi}}\right)^n (\varepsilon)^{\frac{n}{2}-1}
 \end{gather}
 
@@ -109,7 +109,6 @@ $$
 
 #### Question 3.
 
-
 \begin{align}
 E(T)-E(T=0) &= \frac{\pi^2}{6}(k_B T)^2\frac{\partial}{\partial \varepsilon}\left(\varepsilon g(\varepsilon)\right)\bigg|_{\varepsilon=\varepsilon _F}\\
 &\approx 8.356 10^8 eV