Question

If the sixth term of a sequence is 128 and the common ratio is 2, then what is the first term?

Answer 1

common ratio mean geometric sequence


`a_n=a_1(r)^(n-1)`
given tat r=2
and a6=128


`a_6=a_1(2)^(6-1)=128`

`128=a_1(2)^(5)`

`128=a_1(32)`
divide both sides by 32

`4=a_1`
the first term is 4

Answer 2

first term = 4
second term = 4x2=8
3rd = 8x2 =16
4th = 16x2 = 32
5th = 32x2=64
6th = 64x2 = 128

answer: first term = 4