diff --git a/guide/english/mathematics/area-of-a-ellipse/index.md b/guide/english/mathematics/area-of-a-ellipse/index.md
index 3b26aad54c..7608ef7cf3 100644
--- a/guide/english/mathematics/area-of-a-ellipse/index.md
+++ b/guide/english/mathematics/area-of-a-ellipse/index.md
@@ -30,3 +30,4 @@ Area = 1/2 * 2 in * 1/2 * 7 in * π = 11 in<sup>2</sup>
 
 * [Wikipedia](https://en.wikipedia.org/wiki/Ellipse)
 * [Math Is Fun](https://www.mathsisfun.com/geometry/ellipse.html)
+* [Calculus based proof for Area equation](http://www.analyzemath.com/calculus/Integrals/area_ellipse.html)