Question

What is the explicit formula for the sequence below? 4, -12, 36, -108 ...

Answer 1

Answer:

This is a geometry sequence (I.e each term is found by multiplying the same value to the previous term).

T1 = 4

T2 = -12 = T1 X (-3) = 4 X (-3)

T3 = 36 = T2 X (-3) = 4 X (-3)^2

T4 = 108 = T3 X (-3) = 4 X (-3)^3

The general (explicit) formula for the n-th term of this sequence is:

S(n) = 4 X (-3)^(n-1)