A Very Nice Math Olympiad Problem | Solve for x and y | Algebra

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  • Опубліковано 5 лис 2024

КОМЕНТАРІ • 3

  • @msconsult3705
    @msconsult3705 7 днів тому +1

    All solutions for x: x=14, x=-14, x=0, x=-6, x=-8, x=6, x=8

  • @dan-florinchereches4892
    @dan-florinchereches4892 7 днів тому

    Well there is no symmetry I can see and factoring all of this out looks a bit like a pain.
    The form looks a bit like the theorem of Pythagoras. We know a^2+b^2=c^2 if
    a=m^2-n^2
    b=2mn
    c=m^2+n^2 for any m,n integers
    Comparing equations
    x=m^2-n^2
    y=mn
    xy-14=m^2+n^2
    mn(m^2-n^2)-14=m^2+n^2
    (m^2-n^2)(mn-1)=14+2n^2
    1.
    If n=odd right hand side will divide by 4 (7+n^2)*2
    a) m is odd m+n, m-n and mn-1 will divide by 2 each so left hand divides by 8 => 7+n^2 is divisible by 4. If n=2k+1 then 7+n^2=4k^2+4k+8 is always divisible by 4 so this is worth considering (*)
    b) m is even so m+n, m-n and mn-1 are all odd so we also have no solution
    If n is even right hand side will divide by 2 only
    a) m=odd m+n, m-n and mn-1 are all odd and their product is also odd => no solution
    b) m=even then m+n ,m-n are even so Left hand divides by 4 so we need 7+n^2 to be divisible by 4 which is impossible as n is even
    (*) Continuation m=2j+1 and n=2k+1
    (mn-1)(m^2-n^2)=14+2n^2
    ((2j+1)(2k+1)-1)2(j+k)2(j-k)=8k^2+8k+16
    8(2jk+j+k)(j+k)(j-k)=8k^2+8k+16
    (2jk+j+k)(j+k)(j-k)=k^2+k+2
    I don't see any easy way to factor so I will try some values for k.
    Since j,k are integers the product on the left is an integer product but equation k^2+k+2=0 does not have integer solutions so there are no easy conditions to be fulfilled by j and k, maybe just get polynomials in j and k and do long division.
    2j^3k-2jk^3+j^3-jk^2+j^2k-k^3=k^2+k+2
    -k^3(1+2j)-k^2*j+k(2j^3+j^2)+j^3=-k*(1+2j)*(k^2+k+2)+k^2(1+2j)+2k(1+2j)-k^2j+k(2j^3+j^2)+j^3= (-k)(1+2j)(k^2+k+2)+(k^2+k+2-k-2)+k(2j^3+j^2+4j+2)+j^3=(k^2+k+2)(1-k-2jk)+k(2j^3+j^2+4j+1)+j^3-2
    For the relation to gold we need the following conditions
    1-k-2jk=1(1)
    K(2j^3+j^2+4j+1)+J^3-2=0 (2)
    (1) =>k(1+2j)=0 so k =0
    (2) And k=0 => J^3-2=0 no integer solutions
    I am curious about your solution

    • @Miketuteacademy
      @Miketuteacademy 7 днів тому

      The solution he presented in the video is elegant.
      By checking, the answers presented are very much correct.