# Geometry Series | Summary and Q&A

32.0K views
β’
November 27, 2018
by
blackpenredpen
Geometry Series

## TL;DR

Learn how to derive the formula for a power series, specifically the "best friend" series, and understand its relationship with the "mom" series.

## Key Insights

• π The video explains the process of deriving the formula for the "best friend" series using algebraic manipulation.
• β The "best friend" series is an infinite power series that involves adding up terms with increasing powers of X.
• β The "mom" series is a finite version of the geometric series that only includes terms up to X raised to the nth power.
• βΊοΈ The formula for the "best friend" series is 1/(1 - X), which converges when the absolute value of X is less than one.
• β The video mentions the relationship between power series and concepts like natural logarithm and inverse tangent.

## Transcript

okay in this video I'm gonna show you guys how to get the best friend right here from the mom so check this out we are gonna start with the sum first the sum it's going to be this we will have s right we just got some TP s this right here is equal to 1 plus X plus X square plus X plus 3 power plus dot dot remember for the best friend we will have t... Read More

### Q: What is the difference between the "best friend" series and the "mom" series?

The "best friend" series is infinite and involves adding up terms with X raised to increasing powers, while the "mom" series only includes terms up to X raised to the nth power.

### Q: How do you derive the formula for the "best friend" series?

By subtracting equations and simplifying, you can derive the formula 1/(1 - X) for the "best friend" series.

### Q: Are there any restrictions on X for the formula to be valid?

Yes, the absolute value of X must be less than one for the formula 1/(1 - X) to converge and be a valid representation of the "best friend" series.

### Q: Can the formula be modified if the series starts with a different number?

Yes, if the series starts with a different number, you can factor out the common factor and adjust the formula accordingly, but the same principle of 1/(1 - X) applies.

## Summary & Key Takeaways

• The video explains how to derive the formula for a power series called the "best friend" series.

• It compares the "best friend" series to the "mom" series, which is a finite version of the geometric series.

• The goal is to find a formula for the "best friend" series by manipulating equations and multiplying both sides by X.

• By subtracting equations, the video demonstrates how to simplify the equation and derive the final formula for the "best friend" series.