# Math Help - Arithmetic Sequences and Series

1. ## Arithmetic Sequences and Series

I think the text book answer is incorrect here, but wanted to have someone else confirm if this was the case. Thanks in advance.

Q. Find Un, the nth term of sequence: -5, 0, 5, 10,...

Attempt: Un = a + (n - 1)d => -5 + (n - 1)5 = -5 + 5n -5 = 5n - 10

Ans.: (From text book): Un = 5n

2. ## Re: Arithmetic Sequences and Series

Originally Posted by GrigOrig99
I think the text book answer is incorrect here, but wanted to have someone else confirm if this was the case. Thanks in advance.
Q. Find Un, the nth term of sequence: -5, 0, 5, 10,...
Attempt: Un = a + (n - 1)d => -5 + (n - 1)5 = -5 + 5n -5 = 5n - 10
Ans.: (From text book): Un = 5n
I agree with you and not the textbook.
But there is one possible issue: the index.
Some start with $n=0$.
Still with change it would be $a_n=(n-1)5~.$