If the proportional series converges, the absolute value of its common ratio q must be less than 1.
Therefore, when n tends to infinity, the n power of q in the summation formula of equal ratio series tends to 0 (| q |
When q is greater than 1, the proportional series diverges.
Geometric series (also called geometric series): It is a special series. Its characteristic is that the ratio of each term to the previous term is a constant from the second term.
Arithmetic progression is a common series.
Can be expressed by AP. If the difference between each term of a series and its previous term is equal to the same constant of the second term, this series is called arithmetic progression, and this constant is called arithmetic progression's tolerance, which is usually expressed by the letter D ... for example: 1, 3,5,7,9 (2n-1). The general formula of arithmetic progression {an} is: an = a1+(n-1) D. The first n terms and formulas are: sn = n * a1+n (n-1) d/2 or sn = n (a Note: The above integers.