Question

find an equation for the nth term of the geometric sequence where the second and fifth terms are -8 and 512, respectively.

A. an=2*(-4)^n+1
B. an=2*4^n-1
C. an=2*(-4)^n-1
D. an=2*4^n
@dan815 @michele_laino
@nincompoop @campbell @paki @nnesha @e.mccormick

Answer 1

@ash2326 @welshfella @KyanTheDoodle @mathmath333 @misssunshinexxoxo

Answer 2

if a1 is the first term and r = common ratio

second term = a1r = -8
fifth term = a1r^4 = 512


dividing a1r^4 / a1r = 512/-8

r^3 = -64
therefor r = -4

Answer 3

now you can see that
a1*-4 = -8

so now you can find what a1 is

Answer 4

would it be c?

Answer 5

nth term = a1r^(n-1)
so
an = 2*(-4)^(n-1)

Answer 6

yea c is correct

Answer 7

can u help me with another one?