Cube root of ANY number in under 5 seconds Math Trick

This trick allows you to work out the cube root of any number fairly quickly, - and what's more it is easy to learn and remember!
You'll be doing vube roots in your hear - faster than a calcuator.

[tonybarfridge]

For numbers which lie somewhat between cubes, the method becomes less accurate. IE ∛17, =2, +9/(2^2x3)= 9/12=3/4=.75, ans=2.75 actual answer 2.57. Using 3^3 gives 27-17=10, 10/(3^2x3)= 10/27= .37 [don't subtract from 3] (75+37)/2=56, ans= 2.56, much closer than 2.63 or 2.75. To get even closer or exact, subtract 2 from the 9, and add 2 to 10 in the 2nd case. This will produce 2.58 and 2.56 [by subtracting the .44 from 3], just either side of 2.57. So doing just one part would be only .01 off, which could be mentally adjusted.
For 3 digit numbers use the same dual method or vary the differences by 5. In any case averaging the 2 results will achieve better accuracy.

[nilupilu]

I love your accent and the way you teach and also the content. Thank you.

[saadhero]

Want to let you know that your channel is amazing and it helped me get much better at math. Thank you!

[johnryder]

Back to the good old times with Tecmath

[Tanzistr]

Thankyou so much!!!
It was a much needed video

[sukritijha]

Thank you so much I always found it difficult to estimate the cube root of a number in an answer!

[nezumi.]

@tecmath Please pin this:
For those concerned with 8:15 -
See, if you put "6 -1/12" on a calculator, you will still get 5.92 (5.916666...). So, he has just simplified "-1/12" to "11/12". You can still do it either way, however.
Enjoy!

[dreamer]

hello sir, i have a suggestion:- there are millions of indians who wants to learn quantitative aptitude subject (which many of them find it difficult to understand) for various competitive exams in india, since you are an expert in maths it would be of very helpful if you start making videos about that subject.

[LucySteyn-gqbd]

0thank you so much this was super helpful !
( your amazing

[Lulu_user]

This is great my only question is why are we going to the closest number to the actual number is it because u can get the accurate number only with calculator?

[muffin]

Can you explain why you square the closest number and then multiply it by 3 please

[brockormond]

So is this trick using the derivative to solve the cubed? (i.e derivative of x^3 is 3x^2)
Do you do the same with other roots? (ex. x^5, use 5x^4, etc)
Would it be more accurate is you continued using 2nd or 3rd derivatives? (i.e for x^3 it go to 3x^2 to 6x to 6)

[syphon]

How does the 8:15 part work? Could you make a video to elaborate on that?

[larrycho]

I have a question.
From example 8:25, so if like in the case of 'Cubic of 33', in which the answer if positive "3(2/9)", then you just leave as it is. However if the answer is a negative like in the second case 'Cubic of 207', in which the answer is "6(-1/12)", you substract the answer to "6-(1/12)".
I was wondering why that happened. Why the positive one "3(2/9)" does not being added and become "3+(2/9)" too?

I know that this is already the right solution for shortcut, I'm just asking out of curiousity.

[tashiaraynor]

This may be a silly question, but would it work the same for any cube higher than the cube root of 10?

[scmtuk]

What happens if we do this with a number we know is a cube number?

For example, 343?

The nearest cube number to 343 is obviously 343, which is 7³ so the first part of our answer is 7.

Then we find the difference between our number and the nearest cube. In this case, it's 0.
Then we take the 7, square it, and add 3 to get 7²+3 = 49 + 3 = 52.
So, we have 7 + 0/52, which can then be simplified as ... 7.

So, there you go. You've learned how to drive a taxi, by going from A to B, but then going past B, to get to C, then D, and then eventually going around the block to get back to B, because you're an idiot.... and then charge your passenger extra for the extra mileage.

[coreymcdonald]

Can you a video on how to find perfect cube roots for 3 digits numbers??? Example, if I’m given the number 49, 836, 032, how can I easily calculate it so I know the cube root is 368, without a calculator? I can do 2 digit numbers easily, but not 3

[PO-zybo]

Guys hard question what is the cubic root for 215 using this way there is something weird that happens see it by your self

[ksmyth]

I think it would be helpful for most people if you explained why this works. Actually you are calculating (n + alpha)^3 = target, using a known n and then solving for the first order of alpha.

[_ShahriarKabir]

What if a six or seven digit number comes like 1232356