True or False: Every odd number greater than 1 is the smallest member of a primitive Pythagorean triple.
Note: A primitive Pythagorean triple is a triple of positive integers ( a , b , c ) such that a 2 + b 2 = c 2 and g cd ( a , b , c ) = 1 .
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Although not directly related to this question, it's very interesting that the centre of the inscribed circle of a right angled triangle whose sides are a Pythagorean triple has integer coordinates relative to a vertex of the triangle!
We can solve this. If a < b < c, let’s write a = 2n+1 for all n>0, b=2p and c=2p+1.
You can solve the a²+ b² + c² = 0. Replacing a, b and c gives you :
n² + n - p = 0
Δ = 4p + 1 > 0 so there are always 2 solutions.
The positive one is : n = -1/2 + sqrt(p + 1/4) Which can be rewritten as p = n² + n
We have our triplets for n>0
( 2n+1, 2n² + 2n, 2n² + 2n + 1)
And as b and c are consecutive, the gcd of the triplet is always 1.
So all odd numbers >1 are the smallest number of a Pythagorean’s triplet.
. Let a be an odd positive integer greater than 1. Then a 2 + ( 2 a 2 − 1 ) 2 = ( 2 a 2 + 1 ) 2 .
This stems from the "Pythagorean Triples Theorem."
I don't get your triple; the algebra does not work out.
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Corrected, thank you!
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Thanks. Those who previously attempted this question will be marked correct.
8, 15, 17 make a triple, 8 = the smallest member is not odd and gcd (8,15,17)=1 ?! So...
It's false Let a = 1
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But the question stated for every odd number greater than 1. So a CANNOT equal 1.
If we use Euclid's formula for creating Pythagorean triples, but replace natural numbers ( m , n ) where m > n with ( m , m − 1 ) we get that the first term usually denoted by ( m 2 − n 2 ) becomes the difference between two consecutive squares ( m 2 − ( m − 1 ) 2 ) which will simplify to the general term 2 m − 1 for all natural numbers m greater than or equal to 2, thus creating a smallest term that represents the set of all the odd natural numbers.
For every odd number a there exist two perfect squares x and y such that x + a = y , with a < < x Let's consider the case where y = x + 1 The above statement is true in particular for ann odd number a that is also a perfect square. The initial statement then in demonstrated because gcm(x,x+1) is always 1.
Let us first look at c=(b+1)^2, this is b^2+2b+1, 2b+1 describes any odd number for integer b, so this odd number could be the square of any odd number. Let us say this odd number, our odd number, is a=(2b+1)^0.5, we solve for b=((a^2)-1)/2, if we add 1 to get the sum in the Pythagorean triple we get c=((a^2)+1)/2. Now note that c=b+1 so these numbers have a gcd of 1, also do note that a^2 is a multiple of a, so (a^2)+1 and (a^2)-1, both of which have a difference of one, also have a gcd of 1 with a, and since the prime factorisation of the numbers is fundamentally different (no shared primes), and dividing by two would only take away primes (2) without adding primes, a shares no common factors with b or c above 1. We hence have an example where the gcd is one for every odd value above 1.
we can take the cases of --- 1st-3,4&5 2nd-5,12&13 and so on......
It is true if the smallest number is a prime number, not an odd number. What about Pythagorean triple 9, 12 15? gcd(9,12,15) = 3. But, for example, 13, 84, 85 ( easy to prove for the smallest prime number) there exist the primitive Pythagorean triple.
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if a < b < c is a Pythagorean triple for odd a , we know that a 2 = c 2 − b 2 = ( b + c ) ( c − b )
If we let b , c be consecutive integers we get that b + c = 2 b + 1 and c − b = 1 .
Therefore we want to confirm that for every odd a ≥ 3 , there exists a positive integer integer b > a such that a 2 = 2 b + 1 .
Since a 2 is odd and 2 b + 1 can be any odd number, we simply need to make sure that b > a in all cases. a 2 grows faster that 2 b + 1 for 3 ≤ a < b , so if the smallest case works, they all work.
3 2 + 4 2 = 5 2 works, so all off a ≥ 3 are the smallest member of a Pythagorean triple.
Therefore it is True