Answer
a) $\sum_{k=1}^5 k^3$
b) $2(3^2)+2(4^2)+2(5^2)$
Work Step by Step
a) First we notice the form of the general term of our sum: $k^3$.
Then we notice that the sum starts with $k=1$ and ends with $k=5$.
Therefore the sum can be written:
$$1^3+2^3+3^3+4^3+5^3=\sum_{k=1}^5 k^3.$$
b) We rewrite the sum giving $k$ the values from $3$ to $5$:
$$\sum_{k=3}^5 2k^2=2(3^2)+2(4^2)+2(5^2).$$
