Question

What is the equation for a geometric sequence with a first term of 2 and a second term of −8?

an = 2(8)n − 1
an = 2(−8)n − 1
an = 2(4)n − 1
an = 2(−4)n − 1

Answer 1

an = 2 (−4)^ (n − 1)

Explanation:

A geomteric sequence is in the form

an = a1 (r)^(n-1)

a1 =2 and

a2 = -8

-8 = 2 r ^ (2-1)

Divide each side by 2

-4 = r ^1

r = -4

an = 2 (-4) ^ (n-1)