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

1. anonymous

This is my answer. $\sum_{n=0}^{15} (-4+9n)$

2. anonymous

What's the difference between finite and infinite?

3. anonymous

Like how do I determine if it is infinite or finite?

4. geerky42

Your answer is correct. And it's finite, because upper limit is not infinity. You have infinite series if you have something like $$\displaystyle\sum_{i=0}^\infty\dfrac1i$$ (See the infinity symbol?) Is that's what you are asking?

5. geerky42

6. anonymous

|dw:1436566743299:dw|

7. geerky42

1, 2, 3... is infinite, because there is no "end." You just keeping counting and counting. 1, 2, 3, ..., 10 is finite, because you just count till you reach 10.

8. anonymous

One more thing, how would I find the sum of a geometric sequence? What is the easiest way, if there is?

9. anonymous

Oh okay, I just need to be sure about that. :)

10. misty1212

not to butt in, but i have seen these questions where even though it makes no sense, the upper limit is supposed to be infinity not saying it is correct, because it is not, but when it says "assuming the pattern continues" sometimes they want "infinity" at the top

11. anonymous

@misty1212 Yep, that is why it gets so confusing. :(

12. geerky42

13. geerky42

14. geerky42

That mean anything in "..." in any sequence, they just want you to know that patterm remain the same in "...". So if you have something like 1, 2, 3, ..., 6, then by "suggested pattern continues." you would know that entire sequence is 1, 2, 3, *4, 5,* 6 (or at least how sequence behaves), and not 1, 2, 3, *1982374, -123, 64,* 6 something get random here, you know?

15. anonymous

@geerky42 That makes it so much clearer! Thanks! :)

16. geerky42

Glad I cleared that up for you :)