Simple Proof of Pythagorean Theorem using Power of a Point

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Avik Roy
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Simple Proof of Pythagorean Theorem using Power of a Point

Unread post by Avik Roy » Fri Dec 17, 2010 9:45 pm

চিত্রে ACO সমকোণী ত্রিভুজের O কে কেন্দ্র OA ব্যাসার্ধের করে একটি বৃত্ত আঁকা হয়েছে। GH হচ্ছে সেই বৃত্তের ব্যাস এবং AC কে B পর্যন্ত বর্ধিত করা হয়েছে। এক্ষেত্রে C, AB এর মধ্যবিন্দু হবে।
পাওয়ার অফ পয়েন্টের ধারণা থেকে আমরা লিখতে পারি,
$AC.CB = GC.CH$
Hence,
$AC^2 + CO^2 $
$= GC.CH + CO^2$
$ = CO.(GC + CO) + GC.OH$
$ = GO.(GC + CO) $
$ = GO^2$
This implies,
$AC^2 + CO^2 = OA^2$

Well, might be an old one, but it's fun :)
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Moon
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Re: Simple Proof of Pythagorean Theorem using Power of a Poi

Unread post by Moon » Sun Jan 09, 2011 10:17 pm

সুন্দর!
তবে এসব প্রমাণের সমস্যা হল power of point টাইপের কিছুটা advanced idea লাগে। অবশ্য power point আসে similar triangle থেকে, সেই হিসেবে এই প্রমাণটা একই সাথে চমৎকার এবং মোটামুটি সহজ সূত্র থেকেই বলা যায়। :)
আরো অসংখ্য প্রমাণের জন্য এইখানে দেখতে পারেন:
http://www.cut-the-knot.org/pythagoras/
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abir91
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Re: Simple Proof of Pythagorean Theorem using Power of a Poi

Unread post by abir91 » Sun Jan 09, 2011 10:50 pm

আরেকটা প্রমান যেইটা ধনঞ্জয় এবং আমি দেখাইয়া থাকি লোকজনকেঃ

Let, f(x) = sin$^2$ x + cos$^2$ x. Then, f'(x) = 0. So f is a constant function and we have f(0) = 1. Therefore, f(x) = 1 for all x. This implies pythagoras theorem.
Abir

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Moon
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Re: Simple Proof of Pythagorean Theorem using Power of a Poi

Unread post by Moon » Sun Jan 09, 2011 11:09 pm

Wow...super cool! :D
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Avik Roy
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Re: Simple Proof of Pythagorean Theorem using Power of a Poi

Unread post by Avik Roy » Mon Jan 10, 2011 12:13 am

Hmm...
Dhananjay shared that proof with me in facebook. I then went through almost every possible deduction associated with the derivation (like derivatives of Sin and Cosine, rules of compound angle etc)...and I'm satisfied that this proof by non means is Petitio Principi (Begging the question)
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Re: Simple Proof of Pythagorean Theorem using Power of a Poi

Unread post by TIUrmi » Tue Mar 22, 2011 12:50 pm

Nice!... :)
"Go down deep enough into anything and you will find mathematics." ~Dean Schlicter

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