Geometric Series (2024)

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Just as we saw in our previous lesson, P Series Test, there are tests that play an important role in determine convergence of an infinite series.

The Geometric Series Test is one the most fundamental series tests that we will learn.

While the p-series test asks us to find a variable raised to a number, the Geometric Series test is it’s counterpart.

We are looking for a number raised to a variable!

And not just any number, but a fraction called the common ratio, r, and for the series to converge its value must be between negative one and positive one.

Additionally, the geometric series has another incredible feature! While some tests are able to indicate whether a series converges or not, the geometric series test goes above and beyond and provides us with what the series converges to.

Even, Paul’s Online Notes calls the geometric series a special series because it has two important features:

  1. Allows us to determine convergence or divergence,
  2. Enables us to find the sum of a convergent geometric series

Moreover, this test is vital for mastering the Power Series, which is a form of a Taylor Series which we will learn in future lessons.

Geometric Series Video

Geometric Series Example





Geometric Series Overview with Example in Calculus

  • Geometric Series Test Overview
  • Example 1
  • Example 2
  • Example 3
  • Example 4

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Geometric Series (2)
Geometric Series (2024)

FAQs

How do you find the answer to a geometric series? ›

The formula for the sum of a finite geometric series of the form a+ar+ar^2+... +ar^n is given by S = a(1-r^(n+1))/(1-r). This formula can be obtained by setting S = a+ar+ar^2+... +ar^n, multiplying both sides by -r, then adding the two formulas and simplifying.

How to find the limit of a geometric series? ›

Sn=a(1−rn)1−r,for r≠1.

What is the rule for geometric series? ›

A geometric series is a unit series (the series sum converges to one) if and only if |r| < 1 and a + r = 1 (equivalent to the more familiar form S = a / (1 - r) = 1 when |r| < 1).

What is the formula for geometric series sequence? ›

What is the rule for the geometric sequence? Each term of a geometric sequence is formed by multiplying the previous term by a constant number r, starting from the first term a1. Therefore, the rule for the terms of a geometric sequence is an=a1(r)^(n-1).

How to find sums of geometric series? ›

To find the sum of a finite geometric series, use the formula, S n = a 1 ( 1 − r n ) 1 − r , r ≠ 1 , where is the number of terms, is the first term and is the common ratio .

How to solve geometry problems easily? ›

The key to solving geometry problems is to find the formula for the property of the shape and identify the shapes in the diagram. If you have good visualization skills, then you can easily solve geometry problems. But don't get lost in the process and forget to calculate the length of each shape within the diagram.

How to find missing terms in a geometric sequence? ›

Step 1: Find the common ratio of each pair of consecutive terms in the sequence by dividing each term by the term that came before it. Step 2: Multiply the common ratio with the number prior to the first missing number in the sequence. Step 3: Repeat Step 2 for any other missing numbers.

What is a geometric sequence for dummies? ›

Geometric sequences differ from arithmetic sequences. In geometric sequences, to get from one term to another, you multiply, not add. So if the first term is 120, and the "distance" (number to multiply other number by) is 0.6, the second term would be 72, the third would be 43.2, and so on.

How to prove geometric series? ›

How do I prove the geometric series formula?
  1. Write out the sum once.
  2. Write out the sum again but multiply each term by r.
  3. Subtract the second sum from the first. All the terms except two should cancel out.
  4. Factorise and rearrange to make S the subject.

How to solve an infinite geometric series? ›

The general formula for finding the sum of an infinite geometric series is s = a11-r, where s is the sum, a1 is the first term of the series, and r is the common ratio. To find the common ratio, use the formula: a2a1, where a2 is the second term in the series and a1 is the first term in the series.

What is the formula for a finite geometric series? ›

A finite geometric series can be solved using the formula a(1-rⁿ)/(1-r). Sal demonstrates how to derive a formula for the sum of the first 'n' terms of such a series, emphasizing the importance of understanding the number of terms being summed.

How to solve geometric progression? ›

The formula for the nth term of a geometric progression whose first term is a and common ratio is r is: an=arn-1. The sum of n terms in GP whose first term is a and the common ratio is r can be calculated using the formula: Sn = [a(1-rn)] / (1-r). The sum of infinite GP formula is given as: Sn = a/(1-r) where |r|<1.

What are the geometric rules? ›

If two parallel lines are cut by a transversal, then the pairs of corresponding angles are congruent. If two parallel lines are cut by a transversal, then the alternate interior angles are congruent. If two parallel lines are cut by a transversal, then the alternate exterior angles are congruent.

What is the general rule formula for the geometric sequence? ›

The general form of the geometric sequence formula is: an=a1r(n−1), where r is the common ratio, a1 is the first term, and n is the placement of the term in the sequence. Here is a geometric sequence: 1,3,9,27,81,…

How do you find the missing number in a geometric sequence? ›

Step 1: Find the common ratio of each pair of consecutive terms in the sequence by dividing each term by the term that came before it. Step 2: Multiply the common ratio with the number prior to the first missing number in the sequence. Step 3: Repeat Step 2 for any other missing numbers.

How do you find the terms of a geometric series? ›

The terms of a geometric sequence can be found by beginning with the first term and multiplying by the common ratio repeatedly.

How do you find the geometric mean of a series? ›

There are two steps to calculating the geometric mean:
  1. Multiply all values together to get their product.
  2. Find the nth root of the product (n is the number of values).
Dec 2, 2021

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