Question

Consider the following geometric sequence

-5, 20, -30, 40, ...

If the explicit formula for the sequence above is expressed in the form aₙ = b*c^n-1, determine the values of b and c.

Answer 1

b = -5 and c = -4

Explanation:

The common ratio here is r = 20/(-5), or -4, and the first term, a(1), is -5. Thus, the explicit formula is

a(n) = a(1)*r^(n -1) (must use parentheses, as shown)

and so we have a(n) = -5*(-4)^(n - 1). b = -5 and c = -4