Question

Define finite sum and give an example.

Short answer

Answer: A finite sum is the sum of a limited number of terms in a given sequence or series and can be represented as Σ_{i=m}^{n} a_i, where m and n are integers such that m ≤ n, and a_i is the ith term in the sequence. To calculate the finite sum, identify the required terms in the sequence, and then add them together. For example, in the arithmetic sequence 1, 3, 5, 7, 9,..., the finite sum of the first 4 terms is Σ_{i=1}^{4} a_i = 1 + 3 + 5 + 7 = 16.

Step-by-step solution

Definition of Finite Sum

A finite sum refers to the sum of a limited number of terms in a given sequence or series. In mathematical notation, it can be represented as: Σ_{i=m}^{n} a_i = a_m + a_{m+1} + ... + a_n where m and n are integers such that m ≤ n, and a_i is the ith term in the sequence or series.

Example of Finite Sum

Let's take a look at an example. Consider the arithmetic sequence: 1, 3, 5, 7, 9,... To find the sum of the first 4 terms in this sequence, we apply the finite sum formula: Σ_{i=1}^{4} a_i = a_1 + a_2 + a_3 + a_4 In this example, a_i = 2i - 1 for all integer values of i. Thus, the sum can be calculated as: Σ_{i=1}^{4} a_i = (2(1) - 1) + (2(2) - 1) + (2(3) - 1) + (2(4) - 1) = 1 + 3 + 5 + 7 = 16 So, the finite sum of the first 4 terms in this arithmetic sequence is 16.

Key concepts

Sequence and Series

In mathematics, a sequence is a list of numbers that follow a certain pattern. Each number in the list is referred to as a term, and sequences are often denoted using subscript notation, such as \( a_1, a_2, a_3, ... \). A series, on the other hand, is the sum of the terms in a sequence. When we talk about a series, it's essentially about adding up the elements of the sequence to arrive at a total sum.

There are infinite sequences such as the sequence of all natural numbers \( 1, 2, 3, ... \), but for many practical purposes, we deal with a finite portion of a sequence. This leads us to the concept of the finite series, which implies adding up a finite number of terms from a sequence. This is a foundational concept across multiple fields of mathematics, including algebra and calculus, because it allows us to understand and compute cumulative values which are critical in situations such as calculating interest over time or analyzing series circuits in electrical engineering.

Arithmetic Sequence

An arithmetic sequence is a type of sequence where each term after the first is obtained by adding a constant, known as the common difference, to the previous term. This difference can be positive, negative, or zero, leading to increasing, decreasing, or constant sequences, respectively. For example, in the sequence \( 4, 7, 10, 13, ... \), each term increases by 3, which is the common difference.

An important property of an arithmetic sequence is that its terms are equally spaced on the number line. To find the n-th term \( a_n \) of such a sequence, you can use the formula \[ a_n = a_1 + (n - 1)d \] where \( a_1 \) is the first term and \( d \) is the common difference. This formula is excellent for finding any term in the sequence without calculating all preceding ones. Arithmetic sequences are extremely useful in finance for equated instalments, construction for measuring equal distances, and computer science for algorithms with equally distributed iterations.

Summation Notation

The summation notation, also known as sigma notation due to the Greek letter sigma (Σ) used to represent sums, is a convenient way to express the sum of a sequence of terms. This mathematical shorthand simplifies writing and communicating long sums, especially when dealing with sequences.

To read sigma notation, you must identify three main parts: the sigma symbol \( Σ \), the index of summation (often \( i \)), and the upper and lower bounds denoted as \( n \) and \( m \) respectively. For example, \[ Σ_{i=m}^{n} a_i \] indicates the sum of the terms \( a_m, a_{m+1}, ..., a_n \).

Let's take a closer look at how this works with an arithmetic sequence. If you wanted to sum the first four terms of the sequence \( 1, 3, 5, 7 \), you would denote this with \( Σ_{i=1}^{4} (2i - 1) \), where each term \( a_i \) is defined by \( 2i - 1 \), following the arithmetic sequence's rule. The power of summation notation lies in its ability to succinctly represent both simple and intricate sums, catering to a diverse array of mathematical and practical applications.