Use the formula for the sum of the first n terms of a geometric sequence to solve. find the sum of the first 8 terms of the geometric sequence: -8, -16, -32, -64, - ..

d. bc = 12 and ef = 16

step-by-step explanation:

we are given that δabc : δdef such that .

also, it is given that

so, from the options, we need that .

a.

b.

c.  

d.

as, we can see that only option d gives the same ratio as i.e. .

hence, the possible lengths are bc = 12 and ef = 16.