## anonymous one year ago Write the explicit formula that represents the geometric sequence -2, 8, -32, 128

1. freckles

first identify the first term: this is -2 now identify your ratio (just a little more work): divide term by previous term

2. freckles

That is take any term and its very previous term and divide that term by its previous term

3. freckles

for example any of these will give your the common ratio: 8/-2 -32/8 128/-32 that is if this is indeed a geometric sequence which the instructions have identified it as one so all of those will be spit out the same number which is....

4. anonymous

-4

5. freckles

Now just put everything in $a_n=\text{ first term} \cdot \text{ (common ratio)} ^{n-1}$

6. anonymous

a=-2(-4)^n-1?

7. freckles

yes the whole n-1 should be a part of the superscript though like this: a_n=-2(-4)^(n-1) or if I type in pretty latex: $a_n=-2(-4)^{n-1}$

8. anonymous

thanks