diff --git a/education/math/MATH1210 (calc 1)/Max and Min.md b/education/math/MATH1210 (calc 1)/Max and Min.md
index 4ff40a6..43aef58 100644
--- a/education/math/MATH1210 (calc 1)/Max and Min.md	
+++ b/education/math/MATH1210 (calc 1)/Max and Min.md	
@@ -6,3 +6,6 @@ A function $f$ has an absolute minimum at $c$ if $f(c) <= f(x)$. $f(c)$ is the a
 The absolute **minimum** is the smallest possible output value for a function.
 
 - Where the derivative of a function is zero, there is either a peak or a trough.
+
+# Critical Numbers
+A number is considered critical if the output of a function exists and $\dfrac{d}{dx}$ is zero or undefined.