Critical Points

[Nat2663]

I've attached my attempt and found the critical points (0,25), (1,33), (3,-2), (5,71). It seems 3 of these are incorrect, I am unsure which ones and why.

 

[Dr.Peterson]

Please explain how you got the y coordinates. You may just have made arithmetic errors, or there could be something more.

The first, of course, is correct; the others are all wrong in the y.