Question

3. For the following geometric sequence, determine a1 and r and find an explicit formula for the sequence: 2, -6, 18, -54…

a. What is a1?
b. What is the common ratio r?
c. Write an explicit formula for an using the formula for geometric sequences an = a1*(r)n – 1.

Answer 1

Explanation:

a1 is the first term. In this case, 2.

r is the common ratio. Each term is multiplied by -3 to get the next term, so r = -3.

an = 2 (-3)ⁿ⁻¹