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91Ó°ÊÓ

Write a formula for the general term (the nth term) of each arithmetic sequence. Then use the formula for \(a_{n}\) to find \(a_{20}\), the 20 th term of the sequence. \(1,5,9,13, \ldots\)

Short Answer

Expert verified
The 20th term of the sequence is 77

Step by step solution

01

Identify common difference

For an arithmetic sequence, the common difference (d) is the difference between any two successive terms. For the given series 1,5,9,13 it's 5 - 1 = 4.
02

Formulate the nth term formula

The general formula for finding the nth term in an arithmetic sequence is \(a_{n} = a_{1} + (n-1) * d\). So replacing the values \(a_{1}\) with 1 and d with 4 the formula becomes \(a_{n} = 1 + (n-1) * 4\). This formula can be used to find any term in the sequence.
03

Find the 20th term

By using the formula derived in step 2, replace n with 20 to find the 20th term. So, \(a_{20} = 1 + (20-1) * 4\). Calculate the above expression to find the 20th term.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Common Difference
Understanding the common difference is crucial when dealing with arithmetic sequences. It is the engine behind the sequence, pushing each term a fixed amount away from the previous one. In essence, it’s the constant value that you keep adding (or subtracting) to each term to arrive at the next.

In the sequence 1, 5, 9, 13, and so on, if we look closely, each number is 4 units greater than the one before it. This '4' is what we call the common difference, often denoted as 'd'. To identify the common difference, you simply subtract a term from the term that follows it, like so: 5 – 1 = 4. It’s a simple subtraction but one that defines the entire behavior of the sequence. The common difference is the steady rhythm in the music of arithmetic progressions, and it allows us to predict future terms with precision.
Nth Term of an Arithmetic Sequence
When you’re handed an arithmetic sequence and you need to pinpoint the value of a far-reaching term like the 50th, 100th, or even the 1000th term, having to add the common difference repeatedly becomes impractical. This is where the nth term formula comes into play, a formula that acts as a shortcut to leap straight to any term in the sequence.

Formulated as \(a_{n} = a_{1} + (n-1) * d\), it puts the entire sequence into a simple equation. Here, \(a_{1}\) is the first term, 'n' is the term number you’re aiming for, and 'd' is the common difference. To decode any term in the sequence, just plug in the values, and the nth term formula will reveal the answer. It's a powerful tool in the arsenal of anyone dealing with arithmetic sequences, saving time, and providing clarity.
Arithmetic Progression
An arithmetic progression is a lineup of numbers where each term after the first is generated by adding a constant called the common difference to the previous term. It’s like a lineup of dominoes, each one perfectly spaced from the next.

The power of an arithmetic progression lies in its predictability and its structure. Once you know the first term and the common difference, you can map out the entire sequence, no matter how long it is. Mathematics often values concise representation, and arithmetic progression is a classic example of how a simple rule can construct an infinitely long sequence. Whether it's describing a pattern of numbers, counting off intervals, or illustrating rates of change, arithmetic progressions are everywhere, and understanding them can bring order to what might seem like random assortments of numbers.

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Most popular questions from this chapter

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