Theorem:The positive primitive solutions of with y even are , where r and s are arbitrary integers of opposite parity with r>s>0 and gcd(r,s)=1.

Using this theorem, find all solutions of the equation

(hint: write the equation in the form )

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I am not sure how to do this problem. I don't even understand how to get the equation in the hint.

I hope someone can help me out. Thank you!

[also under discussion in math links forum]