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Lauda

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Jul 7th, 2012
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  1. (x^2-1)y'+2xy-4x = 0 koja zadovoljava uslov y(2) = 2:
  2.  
  3. Prvo podijelis citavu jednacinu sa (x^2-1) i onda ti ostane:
  4. y' + (2x/x^2-1)*y = 4x/x^2-1
  5.  
  6. y=u*v ; u = u(x), v = v(x);
  7.  
  8. u'v + uv' + (2x/x^2-1) * uv = 4x/x^2-1
  9.  
  10. u'v + u*(v' + 2x/x^2-1 * v) = 4x/x^2-1
  11.  
  12. Izjednacimo ovo u zagradi sa nulom i imamo:
  13. v' = -2x/x^2-1 * v /:v
  14.  
  15. v'/v = -2x/x^2-1 / integralimo
  16.  
  17. lnv = ln |(x^2-1)^-1| (ovaj integral uradis tako sto uvedes smjenu x^2-1 = t itd.)
  18.  
  19. v = 1/x^2-1
  20.  
  21. u' * 1/x^2-1 = 4x/x^2-1 / * (x^2-1)
  22.  
  23. u' = 4x / integralimo
  24.  
  25. u = 2x^2 + c
  26.  
  27.  
  28. y = u*v => (2x^2+c) * 1/x^2-1 ; (x=2)
  29.  
  30. 2 = (8+c) * 1/3 = (8+c)/3
  31.  
  32. 6 = 8+c => c = -2
  33.  
  34. y = (2x^2-2) * 1/x^2-1
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