[Analysis] fix 3.2.1

semester3/analysis-ii/cheat-sheet-rb/parts/03_diffeq_sol.tex

@@ -70,7 +70,7 @@ $$
 \remark If $\alpha_j = \beta + \gamma i \in \C$ is a root, $\bar{\alpha_j} = \beta - \gamma i$ is too.\\
 To get a real-valued solution, apply:
 $$
-e^{\alpha_j x} = e^{\beta x}\left( \cos(\gamma x) + i \sin(\gamma x) \right)
+e^{\alpha_j x} + e^{\alpha_i x} = e^{\beta x}\left( \cos(\gamma x) + \sin(\gamma x) \right)
 $$
 
 \begin{subbox}{Explicit Homogeneous Solution}