Fix derivative of sqrt(x)

math_differential_calculus.ipynb

@@ -1453,7 +1453,7 @@
     "Note that the power rule works for any $r \\neq 0$, including negative numbers and real numbers. For example:\n",
     "\n",
     "* if $f(x) = \\dfrac{1}{x} = x^{-1}$, then $f'(x)=-x^{-2}=-\\dfrac{1}{x^2}$.\n",
-    "* if $f(x) = \\sqrt(x) = x^{1/2}$, then $f'(x)=\\dfrac{1}{2}x^{-1/2}=-\\dfrac{1}{\\sqrt{x}}$"
+    "* if $f(x) = \\sqrt(x) = x^{1/2}$, then $f'(x)=\\dfrac{1}{2}x^{-1/2}=\\dfrac{1}{2\\sqrt{x}}$"
    ]
   },
   {