In my previous post

DSolve solution of two unknowns

we conclude that Math 10 obtained results fast and that Math 9 did not give the solutions at all after one day. Now I have a problem if there are known constants in the equations, such as a, b, c1 and c2. I know that 8 roots of the characteristic equation are in the form of complex numbers s1,2,3,4=+/-m1+/-n1*i and s5,6,7,8=+/-m2+/-n2*i where i is a (-1)^(1/2).

Is there anyway to obtain analytically result in Mathematica 9 or 10? (I have 9 on win7)

 first=y1''''[x] + a*y1''[x] + c1(y1[x] - y2[x]);
 second=y2''''[x] + b*y2''[x] + c2*y2[x] - c1*(y1[x] - y2[x]);

 DSolve[{first==0,second==0}, {y1[x], y2[x]}, x]
  • $\begingroup$ In case having fixed values is good enough for you this works first = y1''''[x] + y1''[x] + (y1[x] - y2[x]); second = y2''''[x] + y2''[x] + y2[x] - (y1[x] - y2[x]); DSolve[{first == 0, second == 0}, {y1[x], y2[x]}, x] $\endgroup$ – chris Mar 10 '15 at 17:44
  • $\begingroup$ not this chris, but thank you $\endgroup$ – Pipe Mar 10 '15 at 17:54

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