Bonjour,
1)
[tex]f'(5) = \lim_{h\to 0} \frac{f(5+h)-f(5)}{h}\\\\
f'(5) = \lim_{h\to 0} \frac{ \frac{2}{h+6}- \frac{2}{5+1} }{h} \\\\
f'(5) = \lim_{h\to 0} \frac{ \frac{12}{6(h+6)}- \frac{2(h+6)}{6(h+6)} }{h}\\\\
f'(5) = \lim_{h\to 0} \frac{ \frac{-2h}{6h+36} }{h}\\\\
f'(5) = \lim_{h\to 0} \frac{-2h}{h(6h+36)}\\\\
f'(5) = \lim_{h\to 0} \frac{-2}{6h+36}\\\\
\boxed{f'(5) = \frac{-2}{36} = \frac{-1}{18} } [/tex]
Je te laisse faire l'autre ;)
