When we want to write a sum, it can be very inconvenient to have to write it out like so

In these cases, we can use sigma notation:

In sigma notation:

• The $\sum$ is the Greek letter sigma, which is like S in the latin alphabet (for Sum)

• The $k=3$ tells us where the sum should start

• The $17$ at the top tells us where the sum should stop

• The $k^2$ tells us the formula we're summing

Evaluate the following sums:

1. $$\sum _{k=3}^{5}3k-1$$
2. $$\sum _{k=-2}^{1}2k-|k|$$
3. $$\sum _{r=1}^3\frac{(-1{)}^r}{r}$$