I have something like this :
Can someone explain to me how they went from TO
Thank you very much
If you mean from to , they "completed the square".
Now you should recall that " ". Compare and . To be the same, at least for the first two terms, we would have to have so that and so that . That is, to make [tex]u_n^2- u_n[tex] a "perfect square" we must add . Or course, to keep the whole thing the same, we must also subtract . So