Arithmetic Sequences and Series

[odolwa99]

Homework Statement

Just a quick question I was looking to have cross checked…

Q. Find u_n, the nth term of sequence -5, 0, 5, 10,…

Homework Equations

u_n = a + (n-1)d

The Attempt at a Solution

-5 + (n-1)5
-5 + 5n - 5
5n-10

The answer in the book, however, indicates that u_n = 5n. Am I wrong, or are they? Thanks.

 

[gb7nash]

Depends. Are we assuming the first term has index 1? 0? -1? 1000?

If the first term has index -1, then the book is right. Your answer is also right, but you want to state that the first term has index 1.

 

[odolwa99]

I answered two other questions just like it, before this one, and had no problem getting the answer, although the first terms in both of those sequences were positive.

Thanks for the tip, though. I'll mention the index when answering other questions like it in future.