Fixes typo's.

src/2_debye_model_solutions.md

@@ -31,7 +31,7 @@ configure_plotting()
 
 1. For low T, $\beta \rightarrow \infty$. The heat capacity is then given as:
 $$
-C \overset{\mathrm{low \: T}}{\approx} 9Nk_{\mathrm{B}}\left(\frac{T}{T_{D}}\right)^3\int_0^{T_{D}/T}\frac{x^4{\mathrm{e}}^x}{({\mathrm{e}}^x-1)^2}{\mathrm{d}}x.
+C \overset{\mathrm{low \: T}}{\approx} 9Nk_{\mathrm{B}}\left(\frac{T}{T_{D}}\right)^3\int_0^{T/T_D}\frac{x^4{\mathrm{e}}^x}{({\mathrm{e}}^x-1)^2}{\mathrm{d}}x.
 $$
 2. See plot below (shown for $T_{D,1} < T_{D,2}$)
 3. The polarization is related to the direction of the amplitudes of the waves with respect to the direction of the wave.
@@ -43,7 +43,7 @@ $$
 5. The Debye frequency $\omega_D$.
 6. The wavelength is of the order of the interatomic spacing:
 $$
-\lambda = \sqrt{\frac{4}{3}\pi} a.
+\lambda = (\frac{4}{3}\pi)^{1/3} a.
 $$
 
 ```python