Question

Which expression is equivalent to

Answer 1

Answer:

The second expression

Step-by-step explanation:

$\sum_{n=3}^{20}{n(n+1)}=\sum_{n=3}^{20}{(n^2+n)}=\sum_{n=3}^{20}n^2+\sum_{n=3}^{20}n$

You can split up sums.