Update RFC-00xx-automatic-implicit-differentiation.md

Author: 0x00b1

RFC-00xx-automatic-implicit-differentiation.md

@@ -297,7 +297,7 @@ Brent’s method is an extension of the bisection method. It is a root-finding a
 
 ##### Secant Method
 
-Newton’s method for univariate function minimization requires the first and second derivatives $f'$ and $f'''$. In many cases, $f'$ is known but the second derivative is not. The secant method applies Newton’s method using estimates of the second derivative and thus only requires $f′$. This property makes the secant method more convenient to use in practice.
+Newton’s method for univariate function minimization requires the first and second derivatives $f'$ and $f''$. In many cases, $f'$ is known but the second derivative is not. The secant method applies Newton’s method using estimates of the second derivative and thus only requires $f′$. This property makes the secant method more convenient to use in practice.
 
 ##### Quasi-Newton Methods