| Author |
Comment/Response |
Sinval Santos
|
 05/06/02 08:50am
To integrate Sqrt[y-k*x^2] , in relation to x
First: to substitute k after the integration
In[1]:=w1=Integrate[Sqrt[y-k*x^2],x]/.k->2//FullSimplify
Out[1]=(1/4)*(2*x*Sqrt[-2*x^2+y]+I*Sqrt[2]*y*Log[2*(-I*Sqrt[2]*x+ Sqrt[-2*x^2+y])])
In[2]:=w1/.{x->1,y->20}//N
Out[2]=4.39644+15.4928*I (Complex)
Second: to substitute k before the integration
In[1]:=w2=Integrate[(Sqrt[y-k*x^2]/.k->2),x]//FullSimplify
Out[1]=w2=(1/4)*(2*x*Sqrt[-2*x^2+y]+Sqrt[2]*y*ArcTan[(Sqrt[2]*x)/ Sqrt[-2*x^2+y]])
In[2]:=w2/.{x->1,y->20}//N
Out[2]=4.39644 (Real)
Because different results ?
How to avoid this, in symbolic calculation ?
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