Sigma Notation: Geometric Series
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Introduction

    In this lesson, you will learn how to work with sigma notation. Here are the sections in this lesson.

    Before studying sigma notation, it is required that you first have a firm grasp of these mathematical topics.

    esson: Functions
    esson: Geometric Sequences and Series
    esson: Sigma Notation


    Here is a series written in sigma notation.

sigma notation geometric series example

    First, notice how that the variable involves an 'i'. Any variable can be used when dealing with sigma notation. So, an 'i' is no more significant than using an 'n'.

    Let us evaluate the expression for i = -1 to gain our first term. We get...

evaluating first term geometric series

    Evaluating the expression for i = 0 to gain our second term gives us...

evaluating second term geometric series

    Evaluating the expression for i = 1 to gain our third term gives us...

evaluating third term geometric series

    Evaluating the expression for i = 8 to gain our last term gives us...

evaluating last term of geometric series

    So, our sigma notation yields this geometric series.

sigma notation geometric series expanded

    We can find this sum, but the formula is much different than that of arithmetic series. The formula is this.

geometric series sum formula

    We will plug in the values into the formula. Keep in mind that the common ratio -- the r-value -- is equal to a half and the number of terms is 8 - (-1) + 1, which is 10.

sigma notation geometric series sum

    To ensure that you understand this lesson, try this interactive quiz.

    uiz: Sigma Notation: Geometric Series


    Try this quiz, which is related to the sections above.

    uiz: Sigma Notation: Geometric Series


    Try these lessons, which are related to the sections above.

    esson: Functions
    esson: Arithmetic Sequences and Series
    esson: Sigma Notation
    esson: Sigma Notation: Arithmetic Series