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MathGroup Archive 1995

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Re: How to prevent Solve from DSolve?

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg910] Re: How to prevent Solve from DSolve?
  • From: chen at fractal.eng.yale.edu (Richard Q. Chen)
  • Date: Sun, 30 Apr 1995 03:44:36 -0400
  • Organization: Yale University

Sorry I made a typing error in saying that the implicit solution to the ODE

DSolve[2 y[x] + (x + y[x]) y'[x] == 0, y[x], x]

is

f(x,y) = y*(y+2x)^2 = C[1]

It is actually

f(x,y) = y*(y+3x)^2 = C[1]

Verification:

In[1]:= Solve[D[y[x]*(y[x]+3x)^2,x]==0,y'[x]]

                   -2 y[x]
Out[1]= {{y'[x] -> --------}}
                   x + y[x]

In[2]:= 2 y[x] + (x + y[x]) y'[x] == 0/.%[[1]]

Out[2]= True





-- 
Richard Q. Chen
chen at fractal.eng.yale.edu




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