Added fast 2x2 matrix inverse

elec221fs.tex

@@ -372,8 +372,17 @@ \subsection{Interconnection of LTI Systems}
 \end{tabular}
 
 \subsection{Misc. More}
-
+Gaussian Integral:
 \[\int_{-\infty}^{\infty} e^{-a(x+b)^2} dx = \sqrt{\frac{\pi}{a}}\]
+Fast inverse of 2x2 matrix:
+\[\begin{bmatrix}
+a & b\\
+c & d
+\end{bmatrix} ^{-1} = \frac{1}{ad-bc}
+\begin{bmatrix}
+d & -b\\-c & a
+\end{bmatrix}
+\]
 
 
 \end{minipage}
@@ -434,7 +443,7 @@ \subsection{Misc. More}
 
 	\section{Second Order Trial Particular Solutions}
 	\includegraphics[width=0.5\textwidth]{trialparticular}
-	
+
 
 \end{multicols*}