The sigma symbol
signifies summation.
means add up all the numbers
There are several different, similar variations of notation, so that
and
mean essentially the same thing, though the second example means explicitly 'add up all the
from
to
'.
Example: If
find
Example: If
find
Summation in this way has several useful properties:
and
Summation is also linear
This last property can be useful. For the second example above with
we found
We could have used the linearity property to write
There are standard expressions for
and
and
then