## The Summation Symbol

The summation symbol
$\sum$
$\sum x$
$x$
's.
The summation symbol is often accompanied by indices top and bottom which indicate which
$x$
$\sum_{i=3}^7 x_i=x_3+x+4+x_5+x_6+x_7$
$\sum_{i=3}^7 i^2=3^2+4^2+5^2+6^2+7^2$