Question

What is the fifteenth term of the geometric sequence -√5, √10, -2√5...?

Show me how you got to your answer please!

Answer 1

so the nth term is found by plugging that integer into n.

but even though this sequence works. with only three terms, it can very well be the wrong one

Answer 2

No, it just gives three terms. Then is says the possible answers are as follows:

1) -128√5
2) 128√10
3) -16384√5
4) 16384√10

I'm so lost. hahah

Answer 3

\[(-1)^{n+1}\sqrt{5}\sqrt{2^n}\] starts at 0. 15th term: n = 14

Answer 4

\[= (-1)^{14+1} \sqrt{5}\sqrt{2^{14}} = -\sqrt{5}\sqrt{16384}\]
\[= -128\sqrt{5}\]

Answer 5

so my choice was right. we can discuss a bit more how i chose it if u want, but it was really just trial and error and experience.

Answer 6

Thank you so much!! :)

Answer 7

glad i could help :)