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By: a guest on Jun 17th, 2012  |  syntax: None  |  size: 1.70 KB  |  hits: 11  |  expires: Never
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  1. Symbolical mathematical problem (mathematica)
  2. 3/y^4==3/x^4+a/(x+2y)^4
  3.        
  4. ans:    
  5.     3/(r^4 x^4) == 3/x^4 + a/(x + 2 r x)^4
  6.        
  7. ans: Graph and 4 solutions and no its doesn't depend on `a`.
  8.        
  9. In[538]:= eq =
  10.  Eliminate[3/y^4 == 3/x^4 + a/(x + 2 y)^4 && r == y/x, {x, y}]
  11.  
  12. Out[538]= -24 r - 72 r^2 - 96 r^3 + (-45 + a) r^4 + 24 r^5 + 72 r^6 +
  13.   96 r^7 + 48 r^8 == 3
  14.  
  15. In[539]:= r /. Solve[eq && -1 < a < 1, r, Reals]
  16.  
  17. Out[539]= {ConditionalExpression[
  18.   Root[-3 - 24 #1 - 72 #1^2 - 96 #1^3 + (-45 + a) #1^4 + 24 #1^5 +
  19.      72 #1^6 + 96 #1^7 + 48 #1^8 &, 1], -1 < a < 0 ||
  20.    0 < a < Root[-184528125 + 267553125 #1 + 11238750 #1^2 +
  21.        110250 #1^3 - 225 #1^4 + #1^5 &, 1] ||
  22.    Root[-184528125 + 267553125 #1 + 11238750 #1^2 + 110250 #1^3 -
  23.        225 #1^4 + #1^5 &, 1] < a < 1],
  24.  ConditionalExpression[
  25.   Root[-3 - 24 #1 - 72 #1^2 - 96 #1^3 + (-45 + a) #1^4 + 24 #1^5 +
  26.      72 #1^6 + 96 #1^7 + 48 #1^8 &, 2], -1 < a < 0 ||
  27.    0 < a < Root[-184528125 + 267553125 #1 + 11238750 #1^2 +
  28.        110250 #1^3 - 225 #1^4 + #1^5 &, 1] ||
  29.    Root[-184528125 + 267553125 #1 + 11238750 #1^2 + 110250 #1^3 -
  30.        225 #1^4 + #1^5 &, 1] < a < 1],
  31.  ConditionalExpression[
  32.   Root[-3 - 24 #1 - 72 #1^2 - 96 #1^3 + (-45 + a) #1^4 + 24 #1^5 +
  33.      72 #1^6 + 96 #1^7 + 48 #1^8 &, 3],
  34.   0 < a < Root[-184528125 + 267553125 #1 + 11238750 #1^2 +
  35.       110250 #1^3 - 225 #1^4 + #1^5 &, 1]],
  36.  ConditionalExpression[
  37.   Root[-3 - 24 #1 - 72 #1^2 - 96 #1^3 + (-45 + a) #1^4 + 24 #1^5 +
  38.      72 #1^6 + 96 #1^7 + 48 #1^8 &, 4],
  39.   0 < a < Root[-184528125 + 267553125 #1 + 11238750 #1^2 +
  40.       110250 #1^3 - 225 #1^4 + #1^5 &, 1]]}
  41.        
  42. Table[Thread[{a,
  43.     Cases[r /. NSolve[eq, r], r_ /; Im[r] == 0]}], {a, -1, 1,
  44.    0.02}] // ListPlot