explicit formula

Question

Write an explicit formula for the geometric sequence 4, -4/3, 4/9, -4/27,...

Answer 1

A1 = 4

A2 = -4/3

A3 = 4/9

A4 =-4/27

common ratio = r = -1/3

AN = A1r^N-1 = 4r^N-1 = 4(-1/3)^(N-1)

A4 = 4(-1/3)^4-1 = 4(-1/3)^3 = 4(1/27= 4/27