diff --git a/src/2_coordinates.md b/src/2_coordinates.md
index 374432757b533f549fafc2216b2f46be91750d6d..2abb3ae5c7607e0bd8ef3de0273eb43a0a73f0ad 100644
--- a/src/2_coordinates.md
+++ b/src/2_coordinates.md
@@ -21,7 +21,7 @@ The most common coordinates are *Cartesian coordinates*, where we use a
 number $n$ of perpendicular axes. The coordinates corresponding to these
 axes are $x_j$ where $j=1, \ldots, n$.
 
-Cartesian coordinates are simple to describe and operate in. The coordinate axes are 
+Cartesian coordinates are simple to describe and operate on. The coordinate axes are 
 straight lines perpendicular to each other. It is therefore
 very easy to do calculations in Cartesian coordinates. For example,
 the distance $\Delta s$ between two points $(x_1, x_2, \ldots, x_n)$