## anonymous one year ago HELP PRECALC GIVING MEDALS AND BECOMING A FAN 1.)Find an explicit rule for the nth term of the sequence. -4, -8, -16, -32 an = -4 2^(n - 1) an = 2 -4^(n + 1) an = 2 -4^n an = -4 2^n 2.) Find an explicit rule for the nth term of a geometric sequence where the second and fifth terms are -12 and 768, respectively. an = 3 (-4)^(n + 1) an = 3 4^(n - 1) an = 3 (-4)^(n - 1) an = 3 4^n

1. misty1212

HI!!

2. misty1212

you can always check which ones work, but each term in negative, so the number out fron must be negative

3. anonymous

For Question one this is answer: an = -4 • 2n - 1

4. misty1212

if $$n=1$$ you should get $$-4$$ and i think only $-4\times 2^{n-1}$ works

5. anonymous

@misty1212 so is an = -4 • 2^(n - 1) correct?

6. misty1212

yes

7. anonymous

thank you both @misty1212 for the second question I know it isn't an = 3 4^(n - 1) but i hv no idea what it is

8. anonymous

@freckles

9. misty1212

you are supposed to get something that looks like $a_n=a_0\times r^{n-1}$

10. misty1212

$a_2=-12\\ a_5=768$

11. anonymous

is it A? @misty1212

12. misty1212

divide and get $\frac{a_5}{a_2}=\frac{768}{-12}=-64$

13. misty1212

idk i can't eyeball it, we have to do it

14. misty1212

that means $r^3=-64$ so $r=-4$

15. misty1212

then go with C since it is the one that looks like $a_0r^{n-1}$ in this case $$r=-4$$ and $$a_0=3$$ since $3\times (-4)^{2-1}=3\times -4=-12$

16. anonymous

thanks @misty1212