Determine if the sequence below is arithmetic or geometric and determine the common difference / ratio in simplest form. 15,\, 11,\, 7

Answer 1

15, 11, 7, 3, -1, -5, .... is an arithmetic sequence with common difference = d = -4

a1 = 15

an = 15 + (d)(n-1)

a2 = 15 +(-4)(2-1) = 15 -4 = 11

a3 = 15 + (-4)(3-2) = 15-8 = 7

...