Mathematics
posted by Arturo .
I need help with the following problem :
f(n) = n^2 + 4n is O(n^2)

See here:
http://en.wikipedia.org/wiki/Big_O_notation#Formal_definition
You need to find an N and an M > 0 such that
n^2 + 4n < M n^2
for all n > N
This looks like a trivial problem to me...