Square root in 3 seconds - math trick - Free Educational videos for Students in K-12

Square root in 3 seconds - math trick - By tecmath

Transcript


00:0-1	Good day and welcome to Tech Mouth channel . What
00:02	we're going to be having a look at in this
00:03	video is a way of working the square root out
00:05	of numbers . These are gonna be looking where we've
00:08	got the square perfect squares that are occurring less than
00:11	100 but we have to work this out in just
00:13	seconds . Okay , So I'll show you how to
00:16	do this anyway . So First I will give you
00:19	an example , so how fast can you work at
00:20	the square root of 576 ? I'll give you a
00:25	couple of seconds . Okay . Time's up . Did
00:29	you get the answer of positive or -24 If you
00:35	did , That's that's that's great . You got the
00:37	right answer there . If not , I'm going to
00:40	show you how to do this just by the way
00:42	, before getting further square root here . It's really
00:44	important that you actually identify this as a positive or
00:46	negative answer because so negative 24 times negative . 24
00:51	gives us the answer of 526 the same way .
00:54	24 times 24 gives us the answer of 576 .
00:58	So just before I go on , just , just
01:00	make a note of that . Having said that ,
01:02	I'm probably not going to worry about doing the positive
01:05	and miners for the rest of these numbers here .
01:08	I'm just gonna put them down as numbers and you
01:11	can assume that there's a positive of minus there .
01:13	So I'm going to show you how we do this
01:16	and it's going to involve knowing your squares all the
01:19	way up to I've done it up to nine because
01:21	I think you should probably know 10 squared . I
01:23	think you should know these already anyway . I think
01:25	probably most if you will . But you're gonna see
01:27	that . I've got jotted down here , the squares
01:29	, one squared is 12 squared is 43 squared is
01:32	94 square to 16 and so on and so forth
01:35	. We're gonna be using these a fair bit .
01:37	You're also going to notice first off that I've actually
01:40	put the units of these in a different color .
01:43	I'm just going to draw your attention to those Actually
01:46	, right now , when we first are working at
01:48	our answer here , so the way that we do
01:50	it is as follows , the way we work at
01:51	square out of 576 using this is as follows .
01:55	Okay , so first thing we do Is we have
02:00	a look at this particular units , answer the number
02:04	here , 86 . And we're looking for a square
02:07	root here , that corresponds this Or a square ,
02:11	sorry , it's square that corresponds to this . So
02:13	16 does . And 36 does the square root that
02:17	goes alongside of those . We have four When we're
02:21	talking about 16 And we have six when we're talking
02:26	about 36 . So our answer is going to finish
02:29	in a four Or six and we're going to work
02:32	out for sure which one ? This is in a
02:34	little second . But first off we have to work
02:36	out now our uh our first digit , so I'm
02:40	going to cross it . There's two digits . Next
02:42	thing we do , and we just deal directly down
02:45	with this five . Okay . Yeah , we'll have
02:49	a look here along here in our square answers here
02:53	and we're looking for a number that occurs just below
02:57	five . So it's either going to be the number
03:01	five itself or the one closest to five , which
03:04	is under . Okay , so I'm going to go
03:05	along here , you can see 144 is just under
03:09	five and nine is too much . So we're gonna
03:10	be dealing with this for now . The square root
03:12	of four is too to the first part of our
03:15	ETa . Okay . Yeah We're almost there now we
03:21	have to just work out whether or not we're dealing
03:23	with . Is it 24 or 26 is our answer
03:26	? And the way we do this as follows is
03:29	we get out to here and we just multiply it
03:31	by the next number up . Okay . And I
03:34	mean the next number up from two which is three
03:35	, so two times three equals six . Now we
03:40	have a look at this six and pretty much what
03:42	we do is as follows , it is five here
03:46	Is less than the six . We choose the lesser
03:49	number . Okay . If it was more would choose
03:52	the bigger number . Okay , two times three is
03:55	65 is less than six . So we choose the
03:58	lesser number here . So we're about to it's 24
04:03	. Okay , That was a bit of going through
04:04	. I'll tell you what we're going through . A
04:05	couple more of these . You'll pick them up as
04:06	we go along . And then what I'd recommend is
04:09	you'll probably uh be able to start poising it and
04:11	giving it a go . Okay , so let's get
04:15	into another one of these . So what about we
04:17	do ? 1849 . I'm going to work out the
04:22	square root of this . So , first off ,
04:25	once again , what we do is we're looking at
04:27	this nine here . Okay , the nine and the
04:30	number that goes along with our nine could either be
04:33	a three or a seven . You know , these
04:38	complementary numbers add up to 10 to . It's it's
04:40	kind of a handy little thing . The next thing
04:42	I do is I cross out these two numbers .
04:44	Okay , so the answer is going to finish three
04:46	or a seven . Now I look at this 18
04:48	, so 18 and I go down here and I'm
04:50	looking and 16 just occurs below 1825 . Too much
04:55	. So The square is 16 is for the first
04:58	part of a Raanta is four . Okay , four
05:01	times five . Okay , four times five is 20
05:06	. And now I compare this to 18 here .
05:09	So 18 as you'll see is less than 20 .
05:13	So we choose once again the lesson number . Okay
05:17	, so it's a is 43 . You get faster
05:21	and faster and faster at these . Okay , I
05:24	keep practicing them . You you will get used to
05:26	doing them . Okay . Okay , what about one
05:29	more of these ? Uh 3364 . Okay , pause
05:36	it , give it a go . Okay , so
05:38	looking at the last number here , it could be
05:41	either or two or an eight . Okay so let's
05:47	cross out these two digits here and now . What
05:50	we do is we are looking for that first digit
05:52	. Okay so it's going to be a five .
05:54	Okay you're probably working that out really really quickly .
05:56	Okay ? Um because 55 25 66 and 36 that's
06:02	too much , isn't it ? So let's go five
06:05	times six . five times 6 is 30 . is
06:09	bigger Then 30 . So we're going to choose the
06:12	bigger number . We have an eight . So I
06:15	answer is 58 . Okay , What about another 1
06:24	? What about We have a different one here ,
06:27	we'll do uh 2025 . Now this is a nice
06:30	and easy one and you'll see why . Okay pause
06:32	it and give it a go . Okay so 2025
06:37	you're gonna see that can only be a five at
06:39	the end here because there's no other option . Okay
06:41	, cross that out . And then we're looking for
06:44	the number which is going to be occurring under here
06:47	. Okay , so Four squared is going to be
06:49	165 squares too much , so it's going to be
06:51	a four . But this is our answer because we
06:54	don't need to differentiate between whether to five or it's
06:57	just five , isn't it ? So 45 times 45
07:00	. That's our answer . Pretty cool . Right .
07:05	Um Okay , a couple more of these just got
07:08	about three more of these . I'll put them out
07:10	there already been practicing them and say here you go
07:12	. So 5180 for Okay , so our last number
07:18	could either be two or 8 . Okay . Uh
07:23	seven squared is 49 so this is going to be
07:27	a seven . Okay . Uh Seven times eight is
07:30	56 56 is 51 is less than 56 . So
07:35	we're gonna choose the two . Okay This is how
07:40	I start doing these in my head . I'm going
07:41	to start doing the more and more like this will
07:43	do the rest of them like that I reckon .
07:44	So what about 1,444 ? Okay , so the last
07:49	number here could be a two Or it could be
07:53	an eight . Okay so 14 16 squares . Four
07:58	squares too much . Three squares . Good . So
08:00	it's going to be 334 12 , 14 greater than
08:05	12 . So we had to choose the greater number
08:08	which is an eight 38 . Alright , lucky last
08:13	one out of all of them is 8281 . Okay
08:19	so as you see here 81 , well 81 we
08:25	could I'm only gonna look at the last time here
08:27	and it's not attempting to go 81 . Hey wait
08:29	a second , that's nine . I'm only going to
08:30	look at the last digit here . So 81 it
08:33	could be a one or are you doing okay ?
08:42	So what we'll do now is we'll cross that out
08:46	At 82 . Okay , it's 82 . Once again
08:50	this is going to be a nine . Okay ,
08:52	well it's not gonna be a nice because it's not
08:54	necessarily nine so we've got nine . Okay , so
08:59	nine times 10 is 90 82 is less than 90
09:03	so I'm going to choose the lesser value . We've
09:05	got 91 anyway . What did you think of that
09:08	particular trick there ? It's not a bad trick .
09:10	Okay . It does take a bit of getting used
09:12	to , but once you get used to it it's
09:13	actually fairly handy . Okay . And it's a great
09:15	little way of working them out . You start to
09:17	be able to work them out as you see towards
09:18	the end . Much , much , much , much
09:20	, much faster . Okay . And yeah , you
09:22	will make the same mistake . But they everybody does
09:25	this now in the future . A couple of videos
09:27	I am going to be looking at about how to
09:29	work out the are how to calculate squares of any
09:33	number . Okay . The laborious , slow way of
09:35	doing this , but it's not the slowest way ever
09:36	. Just a nice little trick for doing these and
09:39	something you may or may not know how to do
09:40	already . Anyway , Thanks for watching . See you
09:43	next time boy .

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