diff --git a/src/c/funktionen.h b/src/c/funktionen.h
index 28d875e..02a0618 100644
--- a/src/c/funktionen.h
+++ b/src/c/funktionen.h
@@ -47,4 +47,7 @@ float tangent(float x);
 // Function to calculate the arc sine of a value and return the result in radians
 float arcSine(float x);
 
+// Function to calculate the arc cosine of a value and return the result in radians
+float arcCosine(float x);
+
 #endif
\ No newline at end of file