How Do You Find the Critical Numbers of a Function?

[helpm3pl3ase]

Find Critical Numbers of:

F(z) = (z+1)/(z^2+z+1)

Did I start off correctly??

D/dz = - (z + 1)(2z+1)/(z^2+z+1)

I think I derived it correctly? Where do I go from this step?? Thanks

 

[mathman]

D/dz = - (z + 1)(2z+1)/(z^2+z+1)

The derivative is wrong.

It should be

((z^2+z+1)-(z+1)(2z+1))/(z^2+z+1)^2