Explain the mistake that is made.
Evaluate the series $\sum_{k=0}^{3}(-1)^{k} k^{2}$
Solution:
Write out the sum. $\quad \sum_{k=0}^{3}(-1)^{k} k^{2}=-1+4-9$
Simplify the sum. $\sum_{k=6}^{3}(-1)^{k} k^{2}=-6$
This is incorrect. What mistake was made?