Let
be a function which attains in c ∈ ] a , b [ {\displaystyle {}c\in {]a,b[}} a local extremum, and is differentiable there.
f ′ ( c ) = 0 {\displaystyle {}f'(c)=0}
![{\displaystyle f\colon {]a,b[}\longrightarrow \mathbb {R} }](https://wikimedia.org/api/rest_v1/media/math/render/svg/7bcaf3655764f40916a38f2b7b57dd1653da0509)
![{\displaystyle {}c\in {]a,b[}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/893bc6fb00faaeb9f8bf828b68e80a64823b1d6d)
a
local extremum,
and is
differentiable
there.
