diff --git a/paper1/paper1.tex b/paper1/paper1.tex
index e514278..4464040 100644
--- a/paper1/paper1.tex
+++ b/paper1/paper1.tex
@@ -111,7 +111,7 @@ \section{A new spline}
 
 \[
 \begin{aligned}
-\mbox{arm length} & = \tfrac{5}{12}(\sin \theta_a - 0.2\sin 3\theta_a), \quad \mbox{\emph{where}} \\
+\mbox{arm length} & = \tfrac{5}{12}(\cos \theta_a - 0.2\cos 3\theta_a), \quad \mbox{\emph{where}} \\
 \theta_a & = \theta_0 - 0.3 \sin (2\theta_1 - 0.4\sin 2\theta_1) \\
 \end{aligned}
 \]