How do you write log to the base e? I was given a question, find $f'(1)$ of $f(x) = \ln \sqrt{2-x}$.
So I wrote 
$$1/2 \ln (2-x)^{(-1/2)(-1)} = -1/2 \ln (2-x)^{-1/2}$$
$$= -(1/2\ln)/\sqrt{2-x}$$ 
But when I sub in $x = 1$ I get a SYNTAX error, I realised log base e cannot be put in my calculator. I don't know how to put this into my calculator, can anyone help? Thanks!!

Given,
$$ f(x) = \ln \sqrt{2-x} $$
Use chain rule to differentiate.
$$ f^{'}(x) = \frac{1}{\sqrt{2-x}}\frac{1}{2 \sqrt{2-x}} (-1) $$
So, at $x=1$, 
$$f^{'}(1) = \frac{-1}{2} $$
