Taking the derivative and finding critical points did I get it right?

[Femme_physics]

Hey guys, can you just check and tell me if I took the derivative and found the critical points of the function correctly? It strikes as though I've made a mistake somewhere.

http://img405.imageshack.us/img405/4098/funccrit.jpg

 

[gb7nash]

Well, for one thing, $$\frac{4}{x}$$ is not equal to $$\frac{x^{-1}}{4}$$. Fix that before you do anything.

 

[Femme_physics]

Ah. I'm stupid. I forgot my ways. I'll amend that :)

Thanks.