Question

Write the formula for the geometric sequence.
5, 10, 20, 40, …
A. an=40∙2n-1
B. an=40∙2n
C. an=5∙2n-1
D. an=5∙2n

Answer 1

I have no idea how to do this. It would be great if someone could teach me!

Answer 2

a=5,r=10/5=2
\[an=a*r ^{n-1}\]

Answer 3

the general format of a geometric progression is
\[T_{n} = ar^{n-1}\]
where
a = the first term
n = nth term
r = common ration

u already know that the the first term is 5 ...so the
a= 5

now to find (r)
if there is 2 consecutive terms as b , c
\[ r = \frac{ c }{ b }\]

now if u take
b = 5
c= 10
what is r ?

Answer 4

So @***[ISURU]*** is r 0.5?