Arithmetic Sequence
An arithmetic sequence or arithmetical progression is a sequence of numbers such that the differences between successive terms is a constant, d, called the common difference.
8, 3, −2, −7, −12, ...
3 − 8 = −5
−2 − 3 = −5
−7 − (−2) = −5
−12 − (−7) = −5
d = −5.
Nth Term of an Arithmetic Sequence
1If the 1st term is known.
an = a1 + (n − 1) · d
8, 3, −2, −7, −12, ..
an= 8 + (n−1) (−5) = 8 −5n +5 = = −5n + 13
2If the value that occupies any other term of the sequence is known.
an = ak + (n − k) · d
a4 = −7 and d = −5
an = −7+ (n − 4) · (−5)= −7 −5n +20 = −5n + 13
Arithmetic Series
An arithmetic series is the sum of an arithmetic sequence.
Example
Calculate the sum of the first 5 terms of the sequence: 8, 3, −2, −7, −12, ...
