Can you solve the Alice in Wonderland riddle? - Alex Gendler

2,199,247 views ใƒป 2020-11-17

TED-Ed


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

ืชืจื’ื•ื: Ido Dekkers ืขืจื™ื›ื”: Alsa Saal
00:07
After many adventures in Wonderland,
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ืื—ืจื™ ื”ืจื‘ื” ื”ืจืคืชืงืื•ืช ื‘ืืจืฅ ื”ืคืœืื•ืช,
00:10
Alice has once again found herself in the court
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ืืœื™ืก ืžืฆืื” ืืช ืขืฆืžื” ืฉื•ื‘ ื‘ื—ืฆืจ ื”ืžืœื•ื›ื”
00:12
of the temperamental Queen of Hearts.
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ืฉืœ ืžืœื›ืช ื”ืœื‘ื‘ื•ืช ื”ืœื ื™ืฆื™ื‘ื”.
00:15
Sheโ€™s about to pass through the garden undetected,
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ื”ื™ื ืขื•ืžื“ืช ืœืขื‘ื•ืจ ื“ืจืš ื”ื’ืŸ ืžื‘ืœื™ ืฉื™ื–ื”ื• ืื•ืชื”,
00:18
when she overhears the king and queen arguing.
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ื›ืฉื”ื™ื ืฉื•ืžืขืช ืืช ื”ืžืœืš ื•ื”ืžืœื›ื” ืžืชื•ื•ื›ื—ื™ื.
00:21
โ€œItโ€™s quite simple,โ€ says the queen. โ€œ64 is the same as 65, and thatโ€™s that.โ€
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"ื–ื” ื“ื™ ืคืฉื•ื˜," ืื•ืžืจืช ื”ืžืœื›ื”. "64 ื–ื” ืื•ืชื• ื”ื“ื‘ืจ ื›ืžื• 65, ื•ื–ื”ื•."
00:27
Without thinking, Alice interjects. โ€œNonsense,โ€ she says.
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ื‘ืœื™ ืœื—ืฉื•ื‘ ืืœื™ืก ืžืชืขืจื‘ืช. "ืฉื˜ื•ื™ื•ืช," ื”ื™ื ืื•ืžืจืช.
00:31
โ€œIf 64 were the same as 65, then it would be 65 and not 64 at all.โ€
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"ืื 64 ื”ื™ื” ืื•ืชื• ื”ื“ื‘ืจ ื›ืžื• 65, ืื– ื”ื•ื ื”ื™ื” 65 ื•ืœื 64 ื‘ื›ืœืœ."
00:38
โ€œWhat? How dare you!โ€ the queen huffs.
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"ืžื”? ืื™ืš ืืช ืžืขื–ื”!" ื”ืžืœื›ื” ื–ื•ืขืžืช.
00:41
โ€œIโ€™ll prove it right now, and then itโ€™s off with your head!โ€
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"ืื ื™ ืื•ื›ื™ื— ืืช ื–ื” ืขื›ืฉื™ื•, ื•ืื– ืจืืฉืš ื™ื•ืชื–!"
00:44
Before she can protest,
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ืœืคื ื™ ืฉื”ื™ื ื™ื›ื•ืœื” ืœืžื—ื•ืช,
00:46
Alice is dragged toward a field with two chessboard patternsโ€”
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ืืœื™ืก ื ื’ืจืจืช ืœืฉื“ื” ืขื ืฉืชื™ ืชื‘ื ื™ื•ืช ื“ืžื•ื™ื•ืช ืฉื—ืžื˜ --
00:50
an 8 by 8 square and a 5 by 13 rectangle.
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ืจื™ื‘ื•ืข ื‘ืŸ 8 ืขืœ 8 ื•ืžืœื‘ืŸ ื‘ืŸ 5 ืขืœ 13.
00:55
As the queen claps her hands, four odd-looking soldiers approach
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ื›ืฉื”ืžืœื›ื” ืžื•ื—ืืช ื›ืคื™ื™ื, ืืจื‘ืขื” ื—ื™ื™ืœื™ื ืžื•ื–ืจื™ื ืœืžืจืื” ืžืชืงืจื‘ื™ื
01:00
and lie down next to each other, covering the first chessboard.
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ืฉื•ื›ื‘ื™ื ืื—ื“ ืœื™ื“ ื”ืฉื ื™, ื•ืžื›ืกื™ื ืืช ืœื•ื— ื”ืฉื—ืžื˜ ื”ืจืืฉื•ืŸ.
01:03
Alice sees that two of them are trapezoids with non-diagonal sides measuring 5x5x3,
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ืืœื™ืก ืจื•ืื” ืฉืฉื ื™ื™ื ืžื”ื ื˜ืจืคื–ื™ื ื™ืฉืจื™ ื–ื•ื™ืช ืฉืžื™ื“ื•ืชื™ื”ื 5X5X3,
01:11
while the other two are long triangles with non-diagonal sides measuring 8x3.
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ื‘ืขื•ื“ ื”ืฉื ื™ื™ื ื”ืื—ืจื™ื ื”ื ืžืฉื•ืœืฉื™ื ื™ืฉืจื™ ื–ื•ื•ื™ืช ื‘ื’ื•ื“ืœ 8X3.
01:18
โ€œSee, this is 64.โ€
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"ืจื•ืื”? ื–ื” 64."
01:20
The queen claps her hands again.
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ื”ืžืœื›ื” ืžื•ื—ืืช ื›ืคื™ื™ื ืฉื•ื‘.
01:22
The card soldiers get up, rearrange themselves,
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ื—ื™ื™ืœื™ ื”ืงืœืคื™ื ืงืžื™ื, ืžืืจื’ื ื™ื ืืช ืขืฆืžื ืžื—ื“ืฉ,
01:25
and lie down atop the second chessboard.
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ื•ื ืฉื›ื‘ื™ื ืขืœ ืœื•ื— ื”ืฉื—ืžื˜ ื”ืฉื ื™.
01:29
โ€œAnd that is 65."
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"ื•ื–ื” 65."
01:31
Alice gasps. Sheโ€™s certain the soldiers didnโ€™t change size or shape
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ืืœื™ืก ื”ืฉืชื ืงื”. ื”ื™ื ื‘ื˜ื•ื—ื” ืฉื”ื—ื™ื™ืœื™ื ืœื ืฉื™ื ื• ืฆื•ืจื” ืื• ื’ื•ื“ืœ
01:36
moving from one board to the other.
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ื›ืฉืขื‘ืจื• ื‘ื™ืŸ ื”ืœื•ื—ื•ืช.
01:38
But itโ€™s a mathematical certainty that the queen must be cheating somehow.
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ืื‘ืœ ื–ื• ื•ื•ื“ืื•ืช ืžืชืžื˜ื™ืช ืฉื”ืžืœื›ื” ื‘ื˜ื— ืžืจืžื” ืื™ื›ืฉื”ื•.
01:42
Can Alice wrap her head around whatโ€™s wrongโ€” before she loses it?
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ื”ืื ืืœื™ืก ื™ื›ื•ืœื” ืœื”ื‘ื™ืŸ ืžื” ืฉื’ื•ื™ -- ืœืคื ื™ ืฉืชืื‘ื“ ืืช ืจืืฉื”?
01:46
Pause the video to figure it out yourself. Answer in 3.
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ืขืฆืจื• ืคื” ืืช ื”ืกืจื˜ื•ืŸ ื›ื“ื™ ืœื”ื‘ื™ืŸ ื‘ืขืฆืžื›ื. ืชืฉื•ื‘ื” ืขื•ื“ 3.
01:49
Answer in 2
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ืชืฉื•ื‘ื” ืขื•ื“ 2
01:51
Answer in 1
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ืชืฉื•ื‘ื” ืขื•ื“ 1
01:54
Just as things arenโ€™t looking too good for Alice, she remembers her geometry,
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ืžืžืฉ ื›ืฉื”ื“ื‘ืจื™ื ื ืจืื™ื ืœื ื˜ื•ื‘ ืขื‘ื•ืจ ืืœื™ืก, ื”ื™ื ื ื–ื›ืจืช ื‘ืฉื™ืขื•ืจื™ ื”ื’ืื•ืžื˜ืจื™ื”,
01:59
and looks again at the trapezoid and triangle soldier
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ื•ืžื‘ื™ื˜ื” ืฉื•ื‘ ื‘ื—ื™ื™ืœื™ื ื”ื˜ืจืคื–ื™ื™ื ื•ื”ืžืฉื•ืœืฉื™ื
02:03
lying next to each other.
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ืฉืฉื•ื›ื‘ื™ื ืื—ื“ ืœื™ื“ ื”ืฉื ื™.
02:04
They look like they cover exactly half of the rectangle,
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ื”ื ื ืจืื™ื ื›ืื™ืœื• ื”ื ืžื›ืกื™ื ื‘ื“ื™ื•ืง ื—ืฆื™ ืžื”ืžืœื‘ืŸ,
02:08
their edges forming one long line running from corner to corner.
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ื”ืงืฆื•ื•ืช ืœื”ื ื™ื•ืฆืจื™ื ืงื• ืื—ื“ ืืจื•ืš ืฉืจืฅ ืžืคื™ื ื” ืœืคื™ื ื”.
02:12
If thatโ€™s true, then the slopes of their diagonal sides
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ืื ื–ื” ื ื›ื•ืŸ, ืื– ื”ืฉื™ืคื•ืขื™ื ืฉืœ ื”ืฆื“ื“ื™ื ื”ืžืฉื•ืคืขื™ื ืฉืœื”ื
02:16
should be the same.
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ืฆืจื™ื›ื™ื ืœื”ื™ื•ืช ืื•ืชื• ื”ื“ื‘ืจ.
02:17
But when she calculates these slopes
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ืื‘ืœ ื›ืฉื”ื™ื ืžื—ืฉื‘ืช ืืช ื”ืฉื™ืคื•ืขื™ื ื”ืืœื”
02:19
using the tried and true formula "rise over run,"
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ื‘ืฉื™ืžื•ืฉ ื‘ื ื•ืกื—ื” ื”ื™ื“ื•ืขื” "ื’ื•ื‘ื” ืœื—ืœืง ืœืžืจื—ืง,"
02:23
a most curious thing happens.
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ืžืฉื”ื• ืžื•ื–ืจ ืงื•ืจื”.
02:26
The trapezoid soldierโ€™s diagonal side goes up 2 and over 5,
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ื”ืืœื›ืกื•ืŸ ืฉืœ ื”ื—ื™ื™ืœ ื”ื˜ืจืคื–ื™ ืขื•ืœื” 2 ืขืœ ืžืจื—ืง ืฉืœ 5,
02:30
giving it a slope of two fifths, or 0.4.
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ืžื” ืฉื ื•ืชืŸ ืฉื™ืคื•ืข ืฉืœ ืฉืชื™ ื—ืžื™ืฉื™ื•ืช, ืื• 0.4.
02:34
The triangle soldierโ€™s diagonal, however, goes up 3 and over 8,
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ื”ืืœื›ืกื•ืŸ ืฉืœ ื”ื—ื™ื™ืœ ื”ืžืฉื•ืœืฉ, ืขื ื–ืืช, ืขื•ืœื” 3 ืขืœ ืžืจื—ืง 8,
02:40
making its slope three eights, or 0.375.
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ืžื” ืฉื”ื•ืคืš ืืช ื”ืฉื™ืคื•ืข ืฉืœื• ืœืฉืœื•ืฉ ืฉืžื™ื ื™ื•ืช, ืื• 0.375.
02:45
Theyโ€™re not the same at all!
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ื”ื ืœื ืื•ืชื• ื”ื“ื‘ืจ ื‘ื›ืœืœ!
02:47
Before the queenโ€™s guards can stop her,
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ืœืคื ื™ ืฉืžืฉืžืจ ื”ืžืœื›ื” ื™ื›ื•ืœ ืœืขืฆื•ืจ ืื•ืชื”,
02:49
Alice drinks a bit of her shrinking potion to go in for a closer look.
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ืืœื™ืก ืฉื•ืชื” ืžืขื˜ ืžื”ืฉื™ืงื•ื™ ื”ืžื›ื•ื•ืฅ ืฉืœื” ื›ื“ื™ ืœื”ื‘ื™ื˜ ื™ื•ืชืจ ืžืงืจื•ื‘.
02:54
Sure enough, thereโ€™s a miniscule gap between the triangles and trapezoids,
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ื•ื‘ืืžืช, ื™ืฉ ืคืขืจ ื–ืขื™ืจ ื‘ื™ืŸ ื”ืžืฉื•ืœืฉ ืœื˜ืจืคื–,
02:58
forming a parallelogram that stretches the entire length of the board
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ืฉื™ื•ืฆืจ ืžืงื‘ื™ืœื™ืช ืฉืžืชืืจื›ืช ืœื›ืœ ืื•ืจืš ื”ืœื•ื—
03:03
and accounts for the missing square.
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ื•ืžื”ื•ื•ื” ืืช ื”ืจื™ื‘ื•ืข ื”ื—ืกืจ.
03:06
Thereโ€™s something even more curious about these numbers:
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ื™ืฉ ืžืฉื”ื• ืืคื™ืœื• ื™ื•ืชืจ ืžื•ื–ืจ ื‘ื ื•ื’ืข ืœืžืกืคืจื™ื:
03:10
theyโ€™re all part of the Fibonacci series,
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ื”ื ื›ื•ืœื ื—ืœืง ืžืกื“ืจืช ืคื™ื‘ื•ื ืืฆ'ื™,
03:12
where each number is the sum of the two preceding ones.
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ื‘ื” ื›ืœ ืžืกืคืจ ื”ื•ื ื”ืกื›ื•ื ืฉืœ ืฉื ื™ ืืœื• ืฉืœืคื ื™ื•.
03:17
Fibonacci numbers have two properties that factor in here:
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ืœืžืกืคืจื™ ืคื™ื‘ื•ื ืืฆ'ื™ ื™ืฉ ืฉืชื™ ืชื›ื•ื ื•ืช ืฉืžืฉื ื•ืช ืคื”:
03:21
first, squaring a Fibonacci number gives you a value
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ืจืืฉื™ืช, ืจื™ื‘ื•ืข ืฉืœ ืžืกืคืจ ืคื™ื‘ื•ื ืืฆ'ื™ ื ื•ืชืŸ ืขืจืš
03:25
thatโ€™s one more or one less
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ื’ื“ื•ืœ ืื• ืงื˜ืŸ ื‘ืื—ื“
03:27
than the product of the Fibonacci numbers on either side of it.
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ืžื”ืžื›ืคืœื” ืฉืœ ืฉื ื™ ืžืกืคืจื™ ืคื™ื‘ื•ื ืืฆ'ื™ ื”ืฆืžื•ื“ื™ื ืืœื™ื•.
03:31
In other words, 8 squared is one less than 5 times 13,
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ื‘ืžื™ืœื™ื ืื—ืจื•ืช, 8 ื‘ืจื™ื‘ื•ืข ื”ื•ื ืื—ื“ ืคื—ื•ืช ืž 5 ื›ืคื•ืœ 13,
03:35
while 5 squared is one more than 3 times 8.
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ื‘ืขื•ื“ 5 ื‘ืจื™ื‘ื•ืข ื”ื•ื ืื—ื“ ื™ื•ืชืจ ืž 3 ื›ืคื•ืœ 8.
03:40
And second, the ratio between successive Fibonacci numbers is quite similar.
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ื•ืฉื ื™ืช, ื”ื™ื—ืก ื‘ื™ืŸ ืฉื ื™ ืžืกืคืจื™ ืคื™ื‘ื•ื ืืฆ'ื™ ืขื•ืงื‘ื™ื ื”ื•ื ื“ื™ ื“ื•ืžื”.
03:46
So similar, in fact, that it eventually converges on the golden ratio.
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ื›ืœ ื›ืš ื“ื•ืžื”, ืœืžืขืฉื”, ืฉื”ื•ื ืœื‘ืกื•ืฃ ืžืชื›ื ืก ืœื™ื—ืก ื”ื–ื”ื‘.
03:51
Thatโ€™s what allows devious royals to construct slopes
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ื–ื” ืžื” ืฉืžืืคืฉืจ ืœื‘ื ื™ ืžืœื›ื•ืช ืขืจืžื•ืžื™ื™ื ืœื‘ื ื•ืช ืฉื™ืคื•ืขื™ื
03:55
that look deceptively similar.
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ืฉื ืจืื™ื ื“ื•ืžื™ื ื‘ืื•ืคืŸ ืžื˜ืขื”.
03:57
In fact, the Queen of Hearts could cobble together an analogous conundrum
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ืœืžืขืฉื”, ืžืœื›ืช ื”ืœื‘ื‘ื•ืช ื”ื™ืชื” ื™ื›ื•ืœื” ืœื”ื‘ื™ื ื—ื™ื“ื” ื“ื•ืžื”
04:02
out of any four consecutive Fibonacci numbers.
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ืžื›ืœ ืืจื‘ืขื” ืžืกืคืจื™ ืคื™ื‘ื•ื ืืฆ'ื™ ืขื•ืงื‘ื™ื.
04:06
The higher they go, the more it seems like the impossible is true.
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ื›ื›ืœ ืฉื™ื”ื™ื• ื’ื“ื•ืœื™ื ื™ื•ืชืจ, ื™ืจืื” ื™ื•ืชืจ ืฉื”ื‘ืœืชื™ ืืคืฉืจื™ ืืžื™ืชื™.
04:10
But in the words of Lewis Carrollโ€” author of Alice in Wonderland
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ืื‘ืœ ื‘ืขื•ืœื ืฉืœ ืœื•ืื™ืก ืงืจื•ืœ -- ื”ืกื•ืคืจ ืฉืœ ืืœื™ืก ื‘ืืจืฅ ื”ืคืœืื•ืช
04:14
and an accomplished mathematician who studied this very puzzleโ€”
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ื•ื”ืžืชืžื˜ื™ืงืื™ ื”ืžื—ื•ื ืŸ ืฉื—ืงืจ ืืช ื”ื—ื™ื“ื” ื”ื–ื• --
04:19
one canโ€™t believe impossible things.
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ืืกื•ืจ ืœื”ืืžื™ืŸ ืœื“ื‘ืจื™ื ื‘ืœืชื™ ืืคืฉืจื™ื™ื.
ื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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