# 5.2 | Area

Sigma Notation
The sum of $$n$$ terms $$a_1, a_2, \ldots, a_n$$ written as
$$\sum_{i=1}^n a_i = a_1 + a_2 + a_3 + \cdots + a_n$$
where $$i$$ is the index of summation, $$a_i$$ is the $$i$$th term of the sum, and the upper and lower bounds of summation are $$n$$ and 1.
Summation Formulas

1. $$\displaystyle \sum_{i=1}^n c = cn$$
2. $$\displaystyle \sum_{i=1}^n i = \frac{n(n+1)}{2}$$
3. $$\displaystyle \sum_{i=1}^n i^2 = \frac{n(n+1)(2n+1)}{6}$$
4. $$\displaystyle \sum_{i=1}^n i^3 = \frac{n^2(n+1)^2}{4}$$