Reformatted parentheses for natural log in footnote.

index.md

@@ -402,7 +402,7 @@ value of $x$ to plug into our series that will get us the natural log of $u$. We
 setting $u$ equal to the input of each new, combined logarithm and solve for $x$. For the added
 logarithm, set $u$ equal to $1 - x^2$:
 
-[^artanh]: The function $\ln \biggl( \frac{1+x}{1-x} \biggr)$ happens to be the inverse hyperbolic tangent function $ \big( \text{artanh}(x)$ or $\tanh^{-1}(x) \big)$ 
+[^artanh]: The function $\ln \left( \frac{1+x}{1-x} \right)$ happens to be the inverse hyperbolic tangent function $ \big( \text{artanh}(x)$ or $\tanh^{-1}(x) \big)$ 
     multiplied by 2.
 
 $$