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### Course: Class 8 (Old)>Unit 6

Lesson 1: Cube roots using factorisation

# Intro to cube roots

Learn the meaning of cube roots and how to find them. Also learn how to find the cube root of a negative number.

## Want to join the conversation?

• Is there any easy method for finding a square root .... especially for bigger numbers like 1225 or etc..
• Is there any easy way to memorize cube roots? Is there a pattern or some way to help mentally solve cube roots without using a calculator or doing any work?

Thanks
• If the last digit of a cube root is 2 then the unit digit will be 8. If the last digit of a cube root is 3 then the unit digit will be 7. If the last digit of a cube root is 7 then the unit digit will be 3. If the last digit of a cube root is other than 2, 3, 7 and 8 then put the same number as the unit digit.
• What are imaginary numbers? i forget
• An imaginary number is a complex number that can be written as a real number multiplied by the imaginary unit i, which is defined by its property i² = −1. The square of an imaginary number bi is −b². For example, 5i is an imaginary number, and its square is −25. Zero is considered to be both real and imaginary.
• If you are reading this I hope you have a wonderful day and life treats you well, no matter what the situation remember to stay positive and push through cause your a strong person and you'll have good luck soon:)
• Thank you so much! I really needed this today! You're right, life is full of challenges and belly jelly😅 🤬 Please post more encouragement sometimes because it really helps my inner being.
• can a cube root be a negative?
• Yes this is possible. The cube root of a negative number is negative. For example, the cube root of -8 is -2, because (-2)^3 = (-2)(-2)(-2) = -8.

Have a blessed, wonderful day!
• I'm still really confused about cube roots and all. I went through some of the explanations but they used all of these fancy words or numbers and I wish there was an explanation for this which explained it as simply as possible.
• When you cube a number, you raise it to an exponent of 3.
For example: 2^3 = 2*2*2 = 8

A cube root reverses this process. You are being asked to find the number that was originally "cubed".
For example: cube root(8) = 2 because 2^3 = 8

Hope this helps.
• Why are people bragging in the comments about how young they are?? It's not cool to do higher level math, it just puts you under a lot of stress :/
• First off, you do not know if they are telling the truth or not. Secondly, math is individual, so it is possible they understand higher grades than they are in. I do agree that they should not have to brag about it.
• So, you multiply kind of like finding a shapes volume?
• Yes, what you said, but in reverse, is the geometric meaning of taking a cube root. The cube root of a number can be thought of as the edge length of a cube whose volume is that number.

Have a blessed, wonderful day!
• Okay so I've been watching some of these videos but they don't really cover my exact question...

My square root problem:
(2π√(L/32))^2 = (3)^2

So I tried this so many times and I got like, 2 completely different answers and I don't even know if my process to solving this is correct. The answers I got were 281.6 and also -974. So yeah, neither of them look correct and I've been searching FOREVER for a video and so I really would appreciate some help :(

And yes, I know that this video is on cube roots but they first cover square and then now they move to cube, so my question won't be on any of the next few videos so Im asking here.
MAJOR HELP NEEDED!! and if some scholarly person did answer me, could you please write out the steps so I can understand it in the future? THANK YOU IN ADVANCE!
• I'm going to assume that only L is inside the radical.
1) Start by applying the exponent: 4π^2L/1024 = 9
2) Reduce fraction by 4: π^2L/256 ​= 9
3) Multiply both sides by 256: π^2L = 2304
4) Divde both sides by π^2: L = 2304/π^2
If you need an exact answer, this would be it.
5) If you need an estiamted result, then use an estimated value for Pi to whatever precision you need.
-- I'm going to use 3.14: L = 2304/9.8596
-- Finish by dividing: L = 233.68 (approximately)