Question

Which of the following is the formula for this geometric sequence?
1, -3, 9, -27,...
Answer

an = -1(3)n-1

an = 1(-3)n-1

an = 3(-1)n-1

Answer 1

\[
a_n=a_1\times \left(\frac{a_2}{a_1}\right)^{n-1}
\]

Answer 2

\(a_1=1,a_2=-3\)