A point on the graph y = f(x) at which f is differentiable and $f\prime (x)=0$. The term is also used for the number c such that $f\prime (c)=0$. The corresponding value f(c) is a stationary value.

1. (i) If f ′(x)>0 to the left of c and f ′(x)<0 to the right of c, then c is a local maximum;

2. (ii) if f ′(x) < 0 to the left of c and f ′(x) > 0 to the right of c, then c is a local minimum;

3. (iii) f ′(x) has the same sign to the left and to the right of c, then c is a point of inflexion.