Question

Will fan + give medal
What is the 7th term of the geometric sequence where a1 = -5 and a5 = -1,280?

Answer 1

geometric sequence formula is \(\sf \Large a_n=a_1 \times r^{n-1}\)

first thing you have to do is to find the r or the ratio
to find it, plug in your given values into the equation.
\(\sf \Large a_n=a_1 \times r^{n-1}\\ -1280=-5 \times r^{5-1}\)

simplify and solve for r, what will you get ?

Answer 2

256?

Answer 3

\(\sf \Large a_n=a_1 \times r^{n-1}\\ -1280=-5 \times r^{5-1}\\-1280\div -5=r^{4}\\256=r^4\\ r= 4\)

you forget to evaluate \(\sf r^4\) :)
now you have the value for r
you can easily solve for \(\sf a_7\) using the formula

Answer 4

Is it -20,480?

Answer 5

\(\sf \Large a_n=a_1 \times r^{n-1}\\a_7=-5 \times (4)^{6}\\a_7=-5 \times 4096\\ a_7=-20480 \)

looks right ^_^