I have one problem with the solution of the system of two differential equations. I waited hours, but Mathematica didn't give me a solution. Is there any way to obtain the results if we suppose that we know 8 roots of the characteristic equation in the form s1,2,3,4=+/-a1+/-b1*i and s5,6,7,8=+/-a2+/-b2*i? I need a solution where will be 8 unknown constants, of course, which will be obtained for a initial conditions.

DSolve[{y1''''[x] + y1''[x] + y1[x] - y2[x] == 0, 
y2''''[x] + y2''[x] + y2[x] - 2 y1[x] == 0}, {y1[x], y2[x]}, x]
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    $\begingroup$ I get the answer in 0.11 seconds, V 10.02 !Mathematica graphics $\endgroup$ – Nasser Mar 8 '15 at 21:02
  • $\begingroup$ !Mathematica graphics $\endgroup$ – Nasser Mar 8 '15 at 21:13
  • $\begingroup$ I don't know what is a problem with my code, just working and working. Thanks anyway. $\endgroup$ – Pipe Mar 8 '15 at 21:45
  • $\begingroup$ what version of M are you using? Did you try with clean kernel? what OS? $\endgroup$ – Nasser Mar 8 '15 at 22:52
  • $\begingroup$ yes, didn't work... win7 64, math 9 $\endgroup$ – Pipe Mar 8 '15 at 22:54

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