Arithmetic Sequences and Series

In summary, the question asked for the nth term of the sequence -5, 0, 5, 10,... and the formula for finding the nth term is un = a + (n-1)d. The student attempted to solve the problem by plugging in the values, but the answer in the book stated that un = 5n. After considering the index of the first term, it was determined that both answers were correct.
  • #1
odolwa99
85
0

Homework Statement



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

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


Homework Equations



un = 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 un = 5n. Am I wrong, or are they? Thanks.
 
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  • #2
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.
 
  • #3
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.
 

Related to Arithmetic Sequences and Series

1. What is an arithmetic sequence?

An arithmetic sequence is a sequence of numbers in which the difference between consecutive terms is constant. This constant difference is called the common difference and is denoted by d.

2. How do you find the nth term of an arithmetic sequence?

The nth term of an arithmetic sequence can be found using the formula an = a1 + (n-1)d, where an is the nth term, a1 is the first term, and d is the common difference.

3. What is the formula for the sum of an arithmetic series?

The formula for the sum of an arithmetic series is Sn = (n/2)(a1 + an), where Sn is the sum of the first n terms, a1 is the first term, and an is the nth term.

4. How do you find the sum of a finite arithmetic series?

To find the sum of a finite arithmetic series, you can use the formula Sn = (n/2)(a1 + an) or you can use the shortcut formula Sn = (n/2)(2a1 + (n-1)d). Both formulas will give the same result.

5. How can arithmetic sequences and series be applied in real life?

Arithmetic sequences and series can be applied in various real-life situations, such as calculating interest rates, predicting population growth, and analyzing stock market trends. These concepts are also used in fields like physics, engineering, and computer science to model and solve real-world problems.

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