Pre calc help please!!

Question

Classify each sequence and series as arithmetic, geometric, or neither:

a)    1/625 + 1/125 + 1/25 + 1/5 +...

b)     -11 – 2 + 7 + 16 + 25 + 34 + …

c)      420, 84, 16.8, 3.36, …

d)     -8, -3, 2, 7, 12, …

e)     42 + 38 + 32 + 28 + 24 + …

f)       1, 1, 2, 3, 5, …

Answer 1

a) geometric with ratio 1/5

b) arithmetic with difference 9

c) you should try c for yourself; it is similar to one already done

d) arithmetic with difference 5

e) neither....can you see why

f) neither...this is the start of the famous Fibonacci sequence: a_n+2 = a_n+1 + a_n

Answer 2

in "arithmetic" sequences and series, the terms increase or decrease by the constant addition of some value.

In "geometric" sequences and series, the terms increase or decrease as they are multiplied by some constant factor (if the factor is a proper fraction, the series of terms will decrease in value, left-to-right).

Everything else is "other."