Cube Roots in 2 sec using Vedic Math Trick - Free Educational videos for Students in K-12

Cube Roots in 2 sec using Vedic Math Trick - By tecmath

Transcript


00:00	good day and welcome to the Tech Math channel .
00:02	What we're going to be having a look at this
00:03	video as a way of working at cube roots and
00:06	these are for numbers whose cube root value lies between
00:09	one and 100 . It's a really , really good
00:11	little trick . Uh , that's one you can really
00:14	amaze your friends on . It does require a tiny
00:16	little bit of work , but it's once you've actually
00:18	got a couple little things down pat , it's a
00:20	really good little trick for uh , working at cube
00:23	roots almost instantly . Okay , so First off ,
00:27	like a lot of my other videos , I'm going
00:29	to ask you a little question . Uh , how
00:31	fast can you find the cube root of this number
00:34	here ? 21952 . Okay . I'll give you five
00:41	seconds . Okay . Time's up . How did you
00:48	go with that ? Ah now if you got the
00:50	answer of 28 , congratulations . You did really ,
00:55	really good . You got the right answer . Really
00:56	good . Hi , If not don't worry keep watching
01:00	this video because what I'm going to show you right
01:02	now is how to work out the cube root say
01:06	this number here or any number whose cube root value
01:09	lies between one and 100 . So so here we
01:12	go . Before we go though . I think it's
01:15	just before we do that . I'm going to show
01:16	you something . That's it's a really uh it's something
01:19	that it's probably the bit where the work goes .
01:21	Okay so I'll move that across and here's something I
01:24	prepared a little bit earlier . What this is is
01:27	it's a table that shows you all the cubes of
01:30	numbers from one through to nine . So one cubed
01:34	is 12 cubed is 83 cubed is 27 so on
01:37	and so forth . And we're going to use this
01:39	idea to work out cube roots . Okay so like
01:43	I said there is a tiny bit of work but
01:45	it's not too bad . Okay so just bear with
01:48	us . First off , what I want to do
01:50	looking at this is I just want to draw your
01:51	attention to a couple of things . The only drawing
01:54	attention first off to this one here , this particular
01:57	one here , the three cubed is 27 this one
02:00	here the seven cubed and the eight cubed . Now
02:03	I'm just gonna write those numbers down and you might
02:05	be able to see something with these ones are what
02:08	about old uh make these a good black color .
02:10	So we have to and you're gonna see there's an
02:13	aid over here to also ate down there . Um
02:16	So we have this pair two and eight . Both
02:18	of those add up to 10 . So they sort
02:20	of go together pretty well . We also have this
02:21	pair three And seven . And what you're going to
02:25	notice is this if it's one cubed , the answer
02:29	is one and and four cube . The answer is
02:31	four and the answer ends in a four and five
02:34	cube answers . And in the five and the six
02:37	cube the answers and in a six and nine cube
02:39	the answers any nine . But for the to the
02:41	eight , the three and the seven , something slightly
02:45	different happens for the two , it ends in an
02:47	eight and for an eight it ends in A two
02:50	and for the three and ends in a seven and
02:52	for a seven and ends in the three . You
02:54	see that . Okay , so probably the major thing
02:57	you have to remember so far out of these guys
03:01	are these particular ones here , these particular pairs two
03:04	and eight and three and seven . Now with that
03:07	in mind we can work out our cube roots and
03:10	I'll show you how that's done . Now I'm going
03:12	to work it out you know quietly and see if
03:15	you can work out what I do here . Okay
03:16	, this is how you work it out . A
03:21	bit of thinking music and there we go . There's
03:24	our answer . Did you see how I did that
03:27	? Okay . I'll show you it's not too bad
03:30	at all . Now the way this works is this
03:34	so first off what we do and we're working these
03:36	out is we have a look at the last digit
03:40	. Okay so this Did you hear the two Now
03:43	if it's a two we put down you might have
03:46	guessed it . We put down the opposite pair ,
03:49	the pair that goes along with that . The if
03:52	it was at eight would put down to two .
03:54	If it was a seven we put down a three
03:56	. If it was a four would put down a
03:58	four . Okay so hopefully you've got that and then
04:03	we cross out these three digits here And we're left
04:06	with this 21 here . Now what we do is
04:10	we look for a number who is either 21 or
04:14	less ? Which occurs over here ? So 21 or
04:17	less on the answers here is this ? Okay and
04:22	that's too too cute . So the answer is 28
04:27	. Did you get that ? You might you might
04:30	not have I reckon I'm going to go through a
04:32	few more of these . Okay so I'll rub these
04:34	out and I'll give you a couple of other examples
04:38	here . I'll rub that number right out and oh
04:41	I didn't want that to happen . Put him back
04:44	. Oh keep those up there let's let's just leave
04:46	those . And what about I'll give you a different
04:47	example . So what about say what's the cube root
04:52	of ? Um 157,465 four . Okay so What did
05:03	I do ? It's a four and four is not
05:06	a 237 or eight . So what I do Is
05:09	that right down by 4 ? Okay cross out those
05:12	three last digits and then Are 157 would occur about
05:19	here . So the next number under his 100 25
05:21	which is this five cubed . So answer is 54
05:26	. Yeah Hopefully . Uh yeah your understanding that one
05:31	. Hey let's do another example . I'll tell you
05:34	what with this example I'll give you A little moment
05:38	to try and work it out . Okay I'll give
05:40	you a nice easy one . What about 29,791 .
05:47	Okay so do you remember what to do here ?
05:51	It's yeah . Okay , so it's a one .
05:53	Okay . Cross out those three digits . 29 .
05:58	The next one under his 27 which is over here
06:01	? He's a three . All right , sir .
06:04	31 yeah . Pretty good . All right . I'm
06:09	not gonna let you go that easy . What about
06:12	give you this one ? 857,000 375 . Okay ,
06:24	look at that last digit . It's not that 823
06:28	or seven . It's a five . So we're gonna
06:29	put down that five and 857 . The next number
06:36	under that is this 729 which is a nine cubed
06:42	95 is our answer ? Okay . What about one
06:47	last example ? What about this particular 1 ? We
06:51	will put down uh 571,700 and 87 . Okay .
07:05	How are you going with this 1 ? You might
07:08	realize this is one of these special ones . This
07:10	is one of the Yeah with the 71 here ,
07:13	so we're not putting down a seven this time we're
07:15	putting down three . Okay . Last three digits out
07:21	the way . The next number under 5 71 over
07:24	here is 512 . Our answer is 83 . So
07:31	that's how you do this and you can do them
07:32	pretty quick . But as I did say to you
07:34	is a little bit of work with this because as
07:37	you might have realized with this and you're going to
07:39	go away a few people , I can always guarantee
07:41	I'm gonna get the old little comment where people say
07:43	, hey , but I can't work that off the
07:44	top of my head . This one you do have
07:47	to go through and learn the cubes for the numbers
07:50	. One through to nine Here look a few of
07:53	these , a few of them you probably if you're
07:55	okay amounts you probably be fairly familiar with and it's
07:58	not that huge deal . You you pick these up
08:01	pretty quick . I reckon you'll be able to learn
08:02	them in a few minutes . Okay . It's a
08:05	matter of sitting down remembering them and once you can
08:08	actually do that you start to be able to do
08:10	this mentally . Which is really good because I tell
08:13	you you really throw you your mates out . You
08:16	can basically say you work you work out a number
08:19	of the the cube of a number , any number
08:21	between one and 100 and I'll tell you what the
08:22	cube root is . They tried out . Okay they'll
08:26	be amazed when you come out of the number automatically
08:29	they're gonna think you're a genius . Look it's not
08:31	genius it's just a little trick . Okay anyway I
08:35	hope you really like that one . Let's see you
08:37	next time .

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Cube Roots in 2 sec using Vedic Math Trick is a free educational video by tecmath.

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