f(x) = 1/(2x+1)
finding this strangely hard, i think i'm making it a lot harder than it is. help is much appreciated.
$\displaystyle f'(x) = \lim_{h \to 0} \frac{1}{h} \left[ \frac{1}{2(x+h)+1} - \frac{1}{2x+1} \right]$
common denominator to combine the fractions in the [ ... ]
$\displaystyle f'(x) = \lim_{h \to 0} \frac{1}{h} \left[ \frac{(2x+1) - [2(x+h)+1]}{[2(x+h)+1](2x+1)} \right]$
finish it ...