Add electrodinàmica HW2

Change-Id: Icaf0fa41409dfaf79cf919fb20cbe3e7592f8123
diff --git a/quad9/hw_preamble.tex b/quad9/hw_preamble.tex
index 44e88e2..35160bc 100644
--- a/quad9/hw_preamble.tex
+++ b/quad9/hw_preamble.tex
@@ -16,7 +16,7 @@
 \usepackage{enumerate}
 \usepackage{tikz}
 \usepackage[labelfont=bf]{caption}
-\usepackage{siunitx}
+\usepackage[separate-uncertainty=true]{siunitx}
 \usepackage{cancel}
 \usepackage{fancybox}
 \usepackage{multicol}