[Maxima] problem with changevar

Robert Marik marik at mendelu.cz
Mon Aug 4 10:24:36 CDT 2008

Robert Marik <marik <at> mendelu.cz> writes:

> Not let me try changevar
> we do the substitution first and then remove the integral. We should
> get a function equivalent to 2*tan(t)

Sorry, we should get  2/(cos(x))^2, of course.  2* tan(x) is the integral.

> I cannot find the mistake, since I am not familiar with lisp and I
> cannot check the changevar command in sources, but this problem
> disappears if you do substitution x=1/cos(t)  in the integral
> x/sqrt(1-x^2)

The problem disappears also if doing two substitutions in x/(sqrt(x^2-4) , we
can use x=2*t first and then t=1/cos(u). The result is correct. Unfortunatelly,
it seems that we get incorrect answer if we compose these substitution into

Robert M.

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