Question

Which of the following represents a geometric sequence with a common ratio r = 4?

1, 5, 9, 13, 17
3, 12, 16, 64, 256
5, 20, 80, 320, 1,280
128, 32, 8, 2, 0.5

Answer 1

the third option

Explanation:

T2÷T1=4

T3÷T2=4

r=4

Answer 2

The 3rd option is correct,

5, 20, 80, 320, 1280

Explanation:

The geometric sequence is given as,

`a_(n) =a_(1) (r)^(n-1)`

If r = 4,

then the only sequence that corresponds to this is,

the third one with a1 = 5, then,

`a_(2) =a_(1) (4)^(2-1)\\a_(2) =5 (4)\\a_2 = 20\\a_3 = 5(4^2)\\a_3=80\\a_4 = 5(4^3)\\a_4=320\\and \ so \ on`