Write the expression for the general (or nth) term, an, of the geometric sequence.
-5, 10, 20, 40, 80,. . .

Question

Quizplus · Accepted Answer

The common ratio between each term is 2 (i.e. each term is the previous term multiplied by 2), so the general term can be found using the formula an = a1*r^(n-1), where a1 = 5 (the first term), r = 2 (the common ratio), and n is the term number. Therefore, a_n = 5*2^(n-1). This matches option B. The common ratio between consecutive terms is 2 (10/5=2, 20/10=2, 40/20=2, etc.). Therefore, the general term can be found using the formula an = a1 * r^(n-1), where a1 = 5 is the first term and r = 2 is the common ratio. 
So, an = 5 * 2^(n-1). The expression in choice B matches this formula.

Write the Expression for the General (Or Nth) Term, An