Sequences and series formulas4/11/2023 In the example above, the common ratio r is 2, and the scale factor a is 1. Where a n refers to the n th term in the sequenceĪ is the scale factor and r is the common ratio The general form of a geometric sequence can be written as: Using the same number sequence in the previous example, find the sum of the arithmetic sequence through the 5 th term: EX:Ī geometric sequence is a number sequence in which each successive number after the first number is the multiplication of the previous number with a fixed, non-zero number (common ratio). It is also commonly desirable, and simple, to compute the sum of an arithmetic sequence using the following formula in combination with the previous formula to find a n: n × (a 1 + a n) Looking back at the listed sequence, it can be seen that the 5th term, a 5, found using the equation, matches the listed sequence as expected. Using the equation above to calculate the 5 th term: EX: a 5 = a 1 + f × (n-1) It is clear in the sequence above that the common difference f, is 2. The general form of an arithmetic sequence can be written as: This difference can either be positive or negative, and dependent on the sign will result in terms of the arithmetic sequence tending towards positive or negative infinity. Arithmetic SequenceĪn arithmetic sequence is a number sequence in which the difference between each successive term remains constant. Indexing involves writing a general formula that allows the determination of the n th term of a sequence as a function of n. In cases that have more complex patterns, indexing is usually the preferred notation. There are multiple ways to denote sequences, one of which involves simply listing the sequence in cases where the pattern of the sequence is easily discernible. They are particularly useful as a basis for series (essentially describe an operation of adding infinite quantities to a starting quantity), which are generally used in differential equations and the area of mathematics referred to as analysis. Sequences are used to study functions, spaces, and other mathematical structures. A series is convergent if the sequence converges to some limit, while a sequence that does not converge is divergent. Sequences have many applications in various mathematical disciplines due to their properties of convergence. There are many different types of number sequences, three of the most common of which include arithmetic sequences, geometric sequences, and Fibonacci sequences. In a number sequence, the order of the sequence is important, and depending on the sequence, it is possible for the same terms to appear multiple times. The individual elements in a sequence is often referred to as term, and the number of terms in a sequence is called its length, which can be infinite. Accordingly, a number sequence is an ordered list of numbers that follow a particular pattern. In mathematics, a sequence is an ordered list of objects. Then we will investigate different sequences and figure out if they are Arithmetic or Geometric, by either subtracting or dividing adjacent terms, and also learn how to write each of these sequences as a Recursive Formula.Īnd lastly, we will look at the famous Fibonacci Sequence, as it is one of the most classic examples of a Recursive Formula.Example: 1, 3, 5, 7, 9 11, 13. I like how Purple Math so eloquently puts it: if you subtract (i.e., find the difference) of two successive terms, you’ll always get a common value, and if you divide (i.e., take the ratio) of two successive terms, you’ll always get a common value. Then, we either subtract or divide these two adjacent terms and viola we have our common difference or common ratio.Īnd it’s this very process that gives us the names “difference” and “ratio”. And adjacent terms, or successive terms, are just two terms in the sequence that come one right after the other. Well, all we have to do is look at two adjacent terms. It’s going to be very important for us to be able to find the Common Difference and/or the Common Ratio. Comparing Arithmetic and Geometric Sequences
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