Sum of an Arithmetic Series

1
Sum of an Arithmetic Series
Consider the sum of the first 100 positive
integers
Reversing the numbers gives
Adding the two series gives
Simplifying gives
Dividing by 2 gives
2
Formula for the Sum of an Arithmetic Series of n
terms
Consider a General Arithmetic Series of n terms
Reverse the terms
Add the two series
Simplify
Divide by 2
Also note that this can be written as
Which is the same as saying