Series notation and commutativity

In summary, series notation can be tricky to understand, especially when it involves transformations. In this example, the RHS simplifies to -3n because of the definition of multiplication. This can be seen by expanding the sum on the RHS, which results in n terms of 3 being added together.
  • #1
vorophobe
2
0

Homework Statement


I'm trying to wrap my head around series notation, but I'm finding some of the transformations hard to grasp. For example, this one:

Homework Equations


[itex]\Sigma^{n}_{i=1} (2a_{i}-3) = 2\Sigma^{n}_{i=1}a{_i}(-3n)[/itex]

The Attempt at a Solution


In the above expression, I don't understand how you end up with -3n on the RHS. Why can't it just be left as -3?
 
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  • #2
Actually, that is the definition of multiplication!

[itex]3n = \overbrace{3 + 3 + ... + 3}^{n \ times} \ = \ \sum_{i=1}^n3[/itex]
 
  • #3
vorophobe said:

Homework Statement


I'm trying to wrap my head around series notation, but I'm finding some of the transformations hard to grasp. For example, this one:

Homework Equations


[itex]\Sigma^{n}_{i=1} (2a_{i}-3) = 2\Sigma^{n}_{i=1}a{_i}(-3n)[/itex]

The Attempt at a Solution


In the above expression, I don't understand how you end up with -3n on the RHS. Why can't it just be left as -3?

##\sum_{i = 1}^n (2a_i - 3) = \sum_{i = 1}^n 2a_i - \sum_{i = 1}^n 3##

The last sum is 3 + 3 + 3 + ... + 3, a sum with n terms.
 
  • #4
Great replies thank you both!
 

1. What is series notation?

Series notation is a mathematical notation used to represent an infinite sequence of numbers, usually denoted by the symbol ∑. It is used to express the sum of a series of terms, with the index representing the position of each term in the series.

2. How is series notation used in mathematics?

Series notation is commonly used in calculus and other areas of mathematics to express infinite sums or sequences of numbers. It allows for a more concise and compact representation of mathematical expressions, making it easier to work with and manipulate.

3. What is commutativity?

Commutativity is a property of mathematical operations that states that the order in which the operations are performed does not affect the result. In other words, if two numbers are added or multiplied, switching the order of the numbers will not change the result.

4. How is commutativity related to series notation?

In series notation, the commutative property can be applied to the terms of a series. This means that the order in which the terms are added or multiplied does not change the result of the series. This property is especially useful when working with infinite series, as it allows for easier manipulation and evaluation.

5. Can series notation and commutativity be used in real-world applications?

Yes, series notation and commutativity are used in many real-world applications, including finance, physics, and computer science. In finance, series notation is used to calculate compound interest, and in physics, it is used to express the motion of objects in a series of infinitesimal steps. In computer science, commutativity is used in algorithms and data structures to optimize the performance of operations.

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