@XanderHenderson I ultimately downvoted because the asker didn't even put in enough effort to get C(n,3) correct!
@XanderHenderson And I downvoted this one because it too shows hardly any effort for someone who has so much reputation that he/she ought to be able to do more than divide a trivial equation by 4.
@MartinR This is an interesting case. Asker asks X because it was gotten after trying to solve Y. Y was missing from the original question. After it was closed, asker adds in Y. So at first glance it looks like asker is just adding details of the homework question. But no because X was there from the beginning. Funny.
@user21820 Classic X-Y problem! And now the question makes sense, because their question X includes an incorrect conclusion about Y, namely, that given Y, the derivative, set equal to zero (to find critical points), should be $x^2 + 2\lambda$, etc. etc.
This unclear question needs to be closed. The title and question in the body of the post do not match, for one, and the OP has refused to edit the post to correct this mismatch. Plus, the asker has made no attempt prior to posting.
@ZacharySelk, @Did, @user21820, @XanderHenderson, @ProfessorVector. The question I link to immediately above was edited by the OP to change the title from a question about limits, to one about domain and range of a function. They've included no work on their own behalf, except when they edited they included "x+2 = 0, x=-2" (as they were told in comments and in two answers. It deserves to be closed as off topic.
The aforementioned question needs one more delete vote now!
