diff --git a/chap7/chap7.pdf b/chap7/chap7.pdf
index dbd344d..d2d2c96 100644
Binary files a/chap7/chap7.pdf and b/chap7/chap7.pdf differ
diff --git a/chap7/chap7.tex b/chap7/chap7.tex
index f1b8acb..f00cbbd 100644
--- a/chap7/chap7.tex
+++ b/chap7/chap7.tex
@@ -628,11 +628,14 @@ \subsection{Application of the Formalism to \ce{H_2} and \ce{HeH^+}}
 &= \dfrac{ \Braket{12|22}^2}{\varepsilon_1 - \varepsilon_2}
 \end{align}
 \subex{c.}
-
-
-
-
-
+\begin{align}
+\Sigma_{22}^{(2)}(\varepsilon_2) = \dfrac{\Braket{12|22}^2}{\varepsilon_1 - \varepsilon_2} + \dfrac{K_{12}^2}{2(\varepsilon_2 - \varepsilon_1)}
+\end{align}
+$ \therefore $
+\begin{align}
+\varepsilon_2' &= \varepsilon_2 + \Sigma_{22}^{(2)}(\varepsilon_2) \notag\\
+&= {^{N+1}}\tilde{E}_R^{(2)} - {{^N}E}_0^{(2)}
+\end{align}
 
 \subsection{Perturbation Theory and the Green's Function Method}
 \ex{7.13}