Question

find the general term an for the geometric sequence.

a1 = -5 and a2 = 20

Answer 1

Note that, for a geometric series:
\[
\frac{a_{n+1}}{a_{n}}=k
\]For some \(k\).
Hence:
\[
\frac{20}{-5}=-4=k
\]And, our first term \(a_1=-5\), so we have:
\[
a_n=a_1(k)^{n-1}=(-5)(-4)^{n-1}
\]

Answer 2

Ok....so is the answer 20^n-1

Answer 3

Careful, mate, since you can't multiply exponent bases.

Answer 4

ok...so an = (-5)(-4)^n-1