Solution
= Solution
\b[True.] Every term has $k^2\leq n^2$ when $1\leq k\leq n$. Adding these $n$ inequalities gives
$$
0\leq\sum_{k=1}^n k^2\leq n\,n^2=n^3.
$$
The constants $C=1$ and $N=1$ suffice in the definition of <Big O notation>.
= Solution
\b[True.] Every term has $k^2\leq n^2$ when $1\leq k\leq n$. Adding these $n$ inequalities gives
$$
0\leq\sum_{k=1}^n k^2\leq n\,n^2=n^3.
$$
The constants $C=1$ and $N=1$ suffice in the definition of <Big O notation>.