Question

How do you find the missing term in the geometric sequence: `-5, 10, -20, 40, __`?

Answer 1

`-80`

Explanation:

The standard `color(blue)"geometric sequence"` is.

`a,ar,ar^2,ar^3,............ , ar^n`

where r is the common ratio.

and `r=a_2/a_1=a_3/a_2=........ =a_n/(ar_(n-1))`

here `r=10/(-5)=(-20)/10=-2`

Hence to find the missing term, multiply the previous term by r.

`rArra_5=-2xx40=-80`