Series is the sum of a list of numbers that are generating according to some pattern
or rule.
For example, '1+3+5+7+9' is a mathematical series - the sum of the first five odd
numbers.
A series is a description of the operation of adding infinitely many quantities, one
after the other, to a given starting quantity.
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The study of series is a major part
of calculus and its generalization, mathematical analysis. Series are used in most
areas of mathematics, even for studying finite structures (such as in combinatory)
through generating functions. In addition to their ubiquity in mathematics, infinite
series are also widely used in other quantitative disciplines such
as physics, computer science, statistics and finance.
General example of series in real life:
Suppose that your roommate baked an apple pie and left it out on the counter while
she went off to work. Being very fair, you decide to only eat ½ the pie while she's
gone; however, an hour later, you're still hungry, so you eat ½ of what is now left,
or ¼ of the total pie.
Unfortunately for your roommate, her pie is delicious, so you find yourself every
hour again eating half of what's remaining.
As a fraction of the total pie, your pie eating during the eight hours she is at work
looks like this:
½, ¼, 1/8, 1/16, 1/32, 1/64, 1/128, 1/256
Those last slivers of pie were pretty tiny, but you managed.
The list of fractions of pie is a sequence - it's simply a list with commas between
each number.
If you want to know how much of the pie you ate altogether, then you create a
series (a sum), that looks like this:
½ + ¼ + 1/8 + 1/16 + 1/32 + 1/64 + 1/128 + 1/256
By the time your roommate returns, you have polished off 255/256 of the pie.