So you think you know Pythagorean triplets

A Pythagorean triplet a 2 + b 2 = c 2 a^2+b^2=c^2 has the value of a = 97 a = 97 .

Find the sum of the values of b b and c c .


The answer is 9409.

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2 solutions

Maria Kozlowska
May 25, 2015

Euclid's formula is a fundamental formula for generating Pythagorean triples given an arbitrary pair of positive integers m and n with m > n. The formula states that the integers a = m 2 n 2 , b = 2 m n , c = m 2 + n 2 a = m^2 - n^2 ,\ \, b = 2mn ,\ \, c = m^2 + n^2 form a Pythagorean triple. a = 97 = ( m n ) ( m + n ) a = 97 = (m-n)(m+n) 97 is a prime number m n = 1 m = 49 , n = 48 \Rightarrow m-n = 1 \Rightarrow m = 49 ,\ \,n = 48 b + c = ( m + n ) 2 = 9 7 2 = 9409 \Rightarrow b + c = (m+n)^2 = 97^2 = \boxed{9409}

Arian Tashakkor
May 25, 2015

Only thing needed for solving this problem is knowing the fact that 97 97 is a prime.

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Solution:

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a 2 + b 2 = c 2 97 × 97 = ( c b ) ( c + b ) a^2+b^2=c^2 \rightarrow 97\times97 = (c-b)(c+b)

\quad

Now since 97 97 is prime and we know that for positive integral values of b b and c c , ( c + b ) > ( c b ) (c+b) > (c-b) hence it is obligatory that c + b = 9 7 2 c + b = 9409 c+b=97^2 \rightarrow c+b=9409

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There's also a fancier (and definitely much harder solution using the fact that all Pythagorean triplets can be found using the formula below:

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( x , y , z ) = ( d ( a 2 b 2 ) , 2 a b d , d ( a 2 + b 2 ) ) (x,y,z)=(d(a^2-b^2) , 2abd , d(a^2+b^2))

\quad

Where g c d ( a , b ) = 1 gcd(a,b)=1

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