Please help, T/F

1._____ If f'(x) =0 when x=c then f has either a minimum or maximum at x=c.

2._____ If a differentiable function f has a minimum or maximum at x=c, then f'(c)=0.

3._____ If f is continuous on an open interval (a, b) then the f attains maximum or minimum in (a, b).

4._____ If f'(x)=g'(x) then f(x) = g(x).

5._____ If x=c is an inflection point for f, then f (c) must be a maximum or minimum of f.

6._____ f(x) = ax² +bx +c, (with a 0), can have only one critical point.