Re: integral question

minimus wrote:
> 
> Hi,
> 
> When we are taking integral under f(x) of say where (x<y) where y is
some
> postive number,
> I see in the symbolic calculation that we change the letter "x" to
another
> arbitrary letter like "n", and at ther same time
> the dx to dn.  What is this exactly for?

In   int_x^y f(x) dx   the first occurrence of   x  is free and the
second and third are bound.  Some people don't like the same variable
occurring both free and bound in the same formula, so the bound variable
is changed and the formula might become   int_x^y f(n) dn   though the
use of 'n' reads oddly to me.  Note that

   int_x^y f(x) dx = int_x^y f(n) dn

for which reason  x  and  n  are called dummy variables.

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