I decided to watch an MIT OpenCourseWare class on algorithms and the second lecture has me checking my understanding. A link to the lecture is here (http://ocw.mit.edu/courses/electric...ation-recurrences-substitution-master-method/) My question is pretty basic (I think). Right in the beginning of the lecture (2:50 on the video) the prof. writes on the blackboard, 2 n^2 = O(n^3) as an example. I was thinking that should be O(n^2) but then I thought the example statement is true (i.e. 2 n^2 grows slower than n^3 ... and n^4 and n^5 .... ) but the statement with the most information is 2 n^2 = O(n^2). Do you think it was a mistake on the blackboard or he did it to show that the O(n^3) is also true?