## anonymous one year ago Write the sum using summation notation, assuming the suggested pattern continues. -4 + 5 + 14 + 23 + ... + 131

1. freckles

what it is the common difference that is what are the following: 5-(-4)=? 14-5=? 23-14=?

2. anonymous

9 @freckles

3. freckles

right and we know a arithmetic sequence is of the form: $a_n=a_1+d(n-1) \\ \text{ where } a_1 \text{ is first term } \\ \text{ and } d \text{ is common difference } \\ \text{ your answer will be of the form } \sum_{i=1}^{n} a_i=\sum_{i=1}^n [a_1+d(i-1)]$ so the only thing left to figure out is the n for which you get the last term 131

4. freckles

for what n is a_n =131 well just solve: $131=a_1+d(n-1)$ where you found d to be 9

5. anonymous

wait so what do i do next? @freckles

6. freckles

did you find n yet?

7. freckles

for when an is 131

8. freckles

because that is basically the last step besides to plug into the final form

9. anonymous

No I didn't find it

10. freckles

ok well do you still need any help?

11. freckles

I'm not sure if that means you are having a problem solving the equation I gave you or not