The infinite life of pi - Reynaldo Lopes

1,607,196 views ใƒป 2013-07-10

TED-Ed


ืื ื ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ืœืžื˜ื” ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ.

ืชืจื’ื•ื: Ido Dekkers ืขืจื™ื›ื”: benyamin zinshtein
00:13
Try to measure a circle.
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ื ืกื• ืœืžื“ื•ื“ ืžืขื’ืœ.
00:15
The diameter and radius are easy,
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ื”ืงื•ื˜ืจ ื•ื”ืจื“ื™ื•ืก ื–ื” ืงืœ,
00:17
they're just straight lines
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ื”ื ืคืฉื•ื˜ ืงื•ื•ื™ื ื™ืฉืจื™ื
00:18
you can measure with a ruler.
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ืฉืืชื ื™ื›ื•ืœื™ื ืœืžื“ื•ื“ ืขื ืกืจื’ืœ.
00:20
But to get the circumference,
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ืื‘ืœ ื›ื“ื™ ืœืงื‘ืœ ืืช ื”ื”ื™ืงืฃ,
00:21
you'd need measuring tape or a piece of string,
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ืืชื ืชืฆื˜ืจื›ื• ืกืจื˜ ืžื“ื™ื“ื” ืื• ืžืชื™ื›ืช ื—ื•ื˜,
00:24
unless there was a better way.
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ืืœื ืื ื™ืฉ ืœื›ื ื“ืจืš ื˜ื•ื‘ื” ื™ื•ืชืจ.
00:26
Now, it's obvious
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ืขื›ืฉื™ื•, ื–ื” ื‘ืจื•ืจ
00:27
that a circle's circumference would get smaller or larger
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ืฉื”ื”ื™ืงืฃ ืฉืœ ื”ืขื™ื’ื•ืœ ื™ืงื˜ืŸ ืื• ื™ื’ื“ืœ
00:30
along with its diameter,
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ื™ื—ื“ ืขื ื”ื”ื™ืงืฃ,
00:32
but the relationship goes further than that.
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ืื‘ืœ ื”ื™ื—ืก ื”ื•ืœืš ื”ืจื‘ื” ื™ื•ืชืจ ืจื—ื•ืง ืžื–ื”.
00:34
In fact, the ratio between the two,
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ืœืžืขืฉื”, ื”ื™ื—ืก ื‘ื™ืŸ ื”ืฉื ื™ื™ื,
00:36
the circumference divided by the diameter,
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ื”ื”ื™ืงืฃ ื—ืœืงื™ ื”ืงื•ื˜ืจ,
00:39
will always be the same number,
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ืชืžื™ื“ ื™ื”ื™ื• ืื•ืชื• ืžืกืคืจ,
00:41
no matter how big or small the circle gets.
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ืœื ืžืฉื ื” ื›ืžื” ื’ื“ื•ืœ ืื• ืงื˜ืŸ ื”ืขื™ื’ื•ืœ ื ืขืฉื”.
00:44
Historians aren't sure when or how
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ื”ื™ืกื˜ื•ืจื™ื•ื ื™ื ืœื ื‘ื˜ื•ื—ื™ื ืžืชื™ ืื• ืื™ืš
00:46
this number was first discovered,
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ื”ืžืกืคืจ ื”ื–ื” ื ืชื’ืœื” ืœืจืืฉื•ื ื”,
00:48
but it's been known in some form
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ืื‘ืœ ื”ื•ื ื”ื™ื” ื™ื“ื•ืข ื‘ืฆื•ืจื” ื›ืœืฉื”ื™
00:50
for almost 4,000 years.
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ื‘ืžืฉืš 4,000 ืฉื ื” ื›ืžืขื˜.
00:53
Estimates of it appear in the works of ancient Greek,
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ื”ืขืจื›ื•ืช ืฉืœื• ืžื•ืคื™ืขื•ืช ื‘ืขื‘ื•ื“ื•ืช ืฉืœ ื”ื™ื•ื•ื ื™ื ื”ืขืชื™ืงื™ื,
00:55
Babylonian,
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ื‘ื‘ืœื™ื,
00:56
Chinese,
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ืกื™ื ื™ื,
00:57
and Indian mathematicians.
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ื•ืžืชืžื˜ื™ืงืื™ื ื”ื•ื“ื™ื.
00:59
And it's even believed to have been used
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ื•ืืคื™ืœื• ืžืืžื™ื ื™ื ืฉื”ื•ื ื”ื™ื” ื‘ืฉื™ืžื•ืฉ
ื‘ื‘ื ื™ื™ืช ื”ืคื™ืจืžื™ื“ื•ืช ื‘ืžืฆืจื™ื.
01:01
in building the Egyptian pyramids.
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01:03
Mathematicians estimated it
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ืžืชืžื˜ื™ืงืื™ื ื”ืขืจื™ื›ื• ืื•ืชื•
01:04
by inscribing polygons in circles.
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ืขืœ ื™ื“ื™ ืฆื™ื•ืจ ืคื•ืœื™ื’ื•ื ื™ื ืขืœ ื”ืžืขื’ืœ.
01:07
And by the year 1400,
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ื•ืขื“ ืฉื ืช 1400,
01:09
it had been calculated to as far as ten decimal places.
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ื”ื•ื ื—ื•ืฉื‘ ืขื“ ืขืฉืจ ืกืคืจื•ืช ืื—ืจื™ ื”ื ืงื•ื“ื” ื”ืขืฉืจื•ื ื™ืช.
01:13
So, when did they finally figure out the exact value
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ืื–, ืžืชื™ ื”ื ืœื‘ืกื•ืฃ ื™ื“ืขื• ืืช ื”ืขืจืš ื”ืžื“ื•ื™ื™ืง
01:15
instead of just estimating?
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ื‘ืžืงื•ื ื”ืขืจื›ื”?
01:17
Actually, never!
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ืœืžืขืฉื” ืžืขื•ืœื ืœื!
01:20
You see, the ratio
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ืืชื ืžื‘ื™ื ื™ื, ื”ื™ื—ืก
01:21
of a circle's circumference to its diameter
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ืฉืœ ื”ื™ืงืฃ ื”ืžืขื’ืœ ืœืงื•ื˜ืจ ืฉืœื•
01:24
is what's known as an irrational number,
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ื”ื•ื ืžื” ืฉื™ื“ื•ืข ื›ืžืกืคืจ ืœื ืจืฆื™ื•ื ืœื™,
01:26
one that can never be expressed
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ืื—ื“ ืฉืœืขื•ืœื ืื™ ืืคืฉืจ ืœื”ื‘ื™ืข
01:28
as a ratio of two whole numbers.
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ื›ื™ื—ืก ืฉืœ ืฉื ื™ ืžืกืคืจื™ื ืฉืœืžื™ื.
01:31
You can come close,
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ืืชื ื™ื›ื•ืœื™ื ืœื”ื’ื™ืข ืงืจื•ื‘,
01:33
but no matter how precise the fraction is,
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ืื‘ืœ ืœื ืžืฉื ื” ื›ืžื” ืžื“ื•ื™ื™ืง ื”ืฉื‘ืจ,
01:35
it will always be just a tiny bit off.
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ื–ื” ืชืžื™ื“ ื™ืกื˜ื” ืžืขื˜.
01:38
So, to write it out in its decimal form,
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ืื–, ื›ื“ื™ ืœื›ืชื•ื‘ ืื•ืชื• ื‘ืฆื•ืจื” ืขืฉืจื•ื ื™ืช,
01:40
you'd have an on-going series of digits
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ื™ื”ื™ื” ืœื›ื ืกื“ืจื” ืื™ืŸ ืกื•ืคื™ืช ืฉืœ ืกืคืจื•ืช
01:42
starting with
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ืฉืžืชื—ื™ืœื” ื‘
01:43
3.14159
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3,14159
01:46
and continuing
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ื•ืžืžืฉื™ื›ื”
01:47
forever!
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ืœืชืžื™ื“!
01:49
That's why, instead of trying to write out
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ืœื›ืŸ, ื‘ืžืงื•ื ืœื ืกื•ืช ืœื›ืชื•ื‘
01:51
an infinite number of digits every time,
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ืžืกืคืจ ืื™ืŸ ืกื•ืคื™ ืฉืœ ืกืคืจื•ืช ื›ืœ ืคืขื,
01:53
we just refer to it using the Greek letter pi.
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ืื ื—ื ื• ืžืชื™ื™ื—ืกื™ื ืืœื™ื• ื‘ืฉื™ืžื•ืฉ ื‘ืื•ืช ื”ื™ื•ื•ื ื™ืช ืคื™ื™.
01:57
Nowadays, we test the speed of computers
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ื›ื™ื•ื, ืื ื—ื ื• ื‘ื•ื—ื ื™ื ืžื”ื™ืจื•ืช ืฉืœ ืžื—ืฉื‘ื™ื
01:59
by having them calculate pi,
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ื‘ื›ืš ืฉืื ื—ื ื• ื ื•ืชื ื™ื ืœื”ื ืœื—ืฉื‘ ืืช ืคื™ื™,
02:01
and quantum computers have been able
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ื•ืžื—ืฉื‘ื™ื ืงื•ื•ื ื˜ื™ื™ื ื”ื™ื• ืžืกื•ื’ืœื™ื
02:03
to calculate it up to two quadrillion digits.
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ืœื—ืฉื‘ ืื•ืชื• ืขื“ ืฉืชื™ ืงื•ื•ื“ืจืจื™ืœื™ื•ืŸ ืกืคืจื•ืช.
02:06
People even compete to see
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ืื ืฉื™ื ืืคื™ืœื• ืžืชื—ืจื™ื ืœืจืื•ืช
02:08
how many digits they can memorize
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ื›ืžื” ืกืคืจื•ืช ื”ื ื™ื›ื•ืœื™ื ืœืฉื ืŸ
02:09
and have set records for remembering
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ื•ืงื‘ืขื• ืฉื™ืื™ื ืœื–ื›ื™ืจืช
02:11
over 67,000 of them.
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ื™ื•ืชืจ ืž 67,000 ืžื”ืŸ.
02:15
But for most scientific uses,
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ืื‘ืœ ืœืจื•ื‘ ื”ืฉื™ืžื•ืฉื™ื ื”ืžื“ืขื™ื™ื,
02:16
you only need the first forty or so.
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ืืชื ืฆืจื™ื›ื™ื ืืช ื”ืืจื‘ืขื™ื ื”ืจืืฉื•ื ื•ืช.
02:19
And what are these scientific uses?
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ื•ืžื” ื”ื ื”ืฉื™ืžื•ืฉื™ื ื”ืžื“ืขื™ื™ื ื”ืืœื”?
02:21
Well, just about any calculations involving circles,
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ื•ื‘ื›ืŸ, ื‘ืขืจืš ื›ืœ ื—ื™ืฉื•ื‘ ืฉืงืฉื•ืจ ืœืžืขื’ืœื™ื,
02:25
from the volume of a can of soda
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ืžื”ื ืคื— ืฉืœ ืคื—ื™ืช ืกื•ื“ื”
02:27
to the orbits of satellites.
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ืœืžืกืœื•ืœื™ื ืฉืœ ืœื•ื•ื™ื ื™ื.
02:29
And it's not just circles, either.
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ื•ื–ื” ืœื ืจืง ืžืขื’ืœื™ื ืืคื™ืœื•.
02:30
Because it's also useful in studying curves,
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ืžืคื ื™ ืฉื–ื” ื’ื ื™ืขื™ืœ ืœืœื™ืžื•ื“ ืขืงื•ืžื•ืช,
02:33
pi helps us understand periodic or oscillating systems
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ืคื™ื™ ืขื•ื–ืจ ืœื ื• ืœื”ื‘ื™ืŸ ืžืขืจื›ื•ืช ืชืงื•ืคืชื™ื•ืช ืื• ืžืชื ื•ื“ื“ื•ืช
02:36
like clocks,
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ื›ืžื• ืฉืขื•ื ื™ื,
02:37
electromagnetic waves,
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ื’ืœื™ื ืืœืงื˜ืจื•ืžื’ื ื˜ื™ื™ื,
02:39
and even music.
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ื•ืืคื™ืœื• ืžื•ื–ื™ืงื”.
02:40
In statistics, pi is used in the equation
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ื‘ืกื˜ื˜ื™ืกื˜ื™ืงื”, ืคื™ื™ ืžืฉืžืฉ ื‘ืžืฉื•ื•ืื”
02:43
to calculate the area under a normal distribution curve,
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ื›ื“ื™ ืœื—ืฉื‘ ืืช ื”ืฉื˜ื— ืชื—ืช ืขืงื•ืžืช ืคื™ื–ื•ืจ ื ื•ืจืžืœื™ืช,
02:46
which comes in handy for figuring out distributions
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ืžื” ืฉืžื•ืขื™ืœ ืœื”ื‘ื ืช ืคื™ื–ื•ืจื™ื
02:48
of standardized test scores,
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ืฉืœ ืชื•ืฆืื•ืช ืžื‘ื—ื ื™ื ืžื•ืชืืžื•ืช,
02:50
financial models,
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ืžื•ื“ืœื™ื ืคื™ื ื ืกื™ื™ื,
02:51
or margins of error in scientific results.
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ืื• ืžืจื•ื•ื—ื™ ื˜ืขื•ืช ื‘ืชื•ืฆืื•ืช ืžื“ืขื™ื•ืช.
02:54
As if that weren't enough,
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ื•ืื ื–ื” ืœื ื”ื™ื” ืžืกืคื™ืง,
02:55
pi is used in particle physics experiments,
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ืคื™ื™ ืžืฉืžืฉ ื‘ื ื™ืกื•ื™ื™ ืคื™ืกื™ืงืช ื—ืœืงื™ืงื™ื,
02:58
such as those using the Large Hadron Collider,
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ื›ืžื• ืืœื” ื‘ืžืจืกืง ื”ื”ื“ืจื•ื ื™ื ื”ื’ื“ื•ืœ,
03:01
not only due to its round shape,
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ืœื ืจืง ื‘ื’ืœืœ ื”ืฆื•ืจื” ื”ืžืขื’ืœื™ืช ืฉืœื•,
03:03
but more subtly,
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ืืœื ื™ื•ืชืจ ื‘ืขื“ื™ื ื•ืช,
03:04
because of the orbits in which tiny particles move.
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ื‘ื’ืœืœ ืžืกืœื•ืœื™ื ื‘ื”ื ื—ืœืงื™ืงื™ื ื ืขื™ื.
03:07
Scientists have even used pi
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ืžื“ืขื ื™ื ืืคื™ืœื• ื”ืฉืชืžืฉื• ื‘ืคื™ื™
03:09
to prove the illusive notion
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ื›ื“ื™ ืœื”ื•ื›ื™ื— ืืช ื”ืชื—ื•ืฉื” ื”ื—ืžืงืžืงื”
03:11
that light functions as both a particle
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ืฉืื•ืจ ืžืชืคืงื“ ื’ื ื›ื—ืœืงื™ืง
03:13
and an electromagnetic wave,
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ื•ื’ื ื›ื’ืœ ืืœืงื˜ืจื•ืžื’ื ื˜ื™,
03:16
and, perhaps most impressively,
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ื•ืื•ืœื™ ื™ื•ืชืจ ืžืจืฉื™ื,
03:18
to calculate the density of our entire universe,
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ื›ื“ื™ ืœื—ืฉื‘ ืืช ื”ื“ื—ื™ืกื•ืช ื›ืœ ื”ื™ืงื•ื ืฉืœื ื•,
03:21
which, by the way,
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ืฉื“ืจืš ืื’ื‘,
03:23
still has infinitely less stuff in it
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ืขื“ื™ื™ืŸ ื™ืฉ ื‘ื• ื”ืจื‘ื” ืคื—ื•ืช ื—ื•ืžืจ
03:26
than the total number of digits in pi.
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ืžืžืกืคืจ ื”ืกืคืจื•ืช ื‘ืคื™ื™.
ืขืœ ืืชืจ ื–ื”

ืืชืจ ื–ื” ื™ืฆื™ื’ ื‘ืคื ื™ื›ื ืกืจื˜ื•ื ื™ YouTube ื”ืžื•ืขื™ืœื™ื ืœืœื™ืžื•ื“ ืื ื’ืœื™ืช. ืชื•ื›ืœื• ืœืจืื•ืช ืฉื™ืขื•ืจื™ ืื ื’ืœื™ืช ื”ืžื•ืขื‘ืจื™ื ืขืœ ื™ื“ื™ ืžื•ืจื™ื ืžื”ืฉื•ืจื” ื”ืจืืฉื•ื ื” ืžืจื—ื‘ื™ ื”ืขื•ืœื. ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ื”ืžื•ืฆื’ื•ืช ื‘ื›ืœ ื“ืฃ ื•ื™ื“ืื• ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ ืžืฉื. ื”ื›ืชื•ื‘ื™ื•ืช ื’ื•ืœืœื•ืช ื‘ืกื ื›ืจื•ืŸ ืขื ื”ืคืขืœืช ื”ื•ื•ื™ื“ืื•. ืื ื™ืฉ ืœืš ื”ืขืจื•ืช ืื• ื‘ืงืฉื•ืช, ืื ื ืฆื•ืจ ืื™ืชื ื• ืงืฉืจ ื‘ืืžืฆืขื•ืช ื˜ื•ืคืก ื™ืฆื™ืจืช ืงืฉืจ ื–ื”.

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