The sigma symbolsignifies summation.

means add up all the numbersThere are several different, similar variations of notation, so thatandmean essentially the same thing, though the second example means explicitly ‘add up all thefromto‘.

Example: Iffind

Example: Iffind

Summation in this way has several useful properties:

and

Summation is also linear

This last property can be useful. For the second example above withwe found We could have used the linearity property to write

There are standard expressions forand

and

then