The question: find the point on the plane that is closest to the point .

So I guess in math terms the problem is to find where

It's clear that

And of course, what you're supposed to do is set them equal to zero and solve. Only problem is, I have no clue how to do that. Any help appreciated. Thanks in advance.

Edit: Never mind, is it as stupid as I think it is?

Is that the solution? If so, I think I should bash my head against a wall.