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# Worked example: Cube root of a negative number

Learn how to find the cube root of negative 512 by breaking it down into prime factors. When we find groups of three of the same factor, we know that's a factor of the cube root. It helps to remember that -1*-1*-1 is -1, so the cube root of -1 is itself. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• i still do not get it :( please explain more, for example where did he get the 2's?
• I find it easiest just to Guess and Check....What number cubed equals -512? I find people start to memorize the common ones after a bit.
• How do i get the cube root of a number like 4?
• The cube root won't be an exact number, if that's what you're asking.

To get an idea of what it might be,
4 is found in between 1 and 8
This means that the cube root of 4 will be in between cube root of 1 and cube root of 8, or in other words, between 1 and 2.
4 is closer to 1 than 8 (4-1=3 while 8-4=4). so the cube root of 4 will be a number in between 1 and 1.5
• Why is reading the comments much more fun
• Reading the comments can be more enjoyable for various reasons. Sometimes, viewers share their own insights, ask thought-provoking questions, or provide alternative perspectives that can enhance our understanding of the topic. Additionally, it can create a sense of community among learners, as we get to engage with others who are also grappling with the same concepts. Furthermore, there might be some humor or interesting anecdotes shared in the comments, making the learning experience more enjoyable and relatable. Overall, while the video itself provides valuable instruction, the comments section often adds another layer of richness to the learning process.
(1 vote)
• I am grade 4 I did square roots. and I did cube roots
• the cube root does not have to be perfect?
• That is true just like square roots. Any whole number that is not 1, 8, 27, 64, 125 ... is not a perfect cube.
• 😨So hard
• How to simplify the cube root of 9317 ... any ideas?
• The simplified cube root of that number is 11 3√ 7
• 2x3=6 not 8 rite?
• 2 x 3 can either be thought of as 2 + 2 + 2 or as 3 + 3. Or stating that another way, 2 groups of 3 items or 3 groups that each have 2 items and it does equal 6.
To cube something is to multiply it by itself, 2 x 2 x 2 = 4 x 2 = 8. It is written 2^3 = 8
• At , couldn't Sal have stop factoring at 64 since 8x8=64?