On Thu, 29 May 2008 19:08:07 +0200, "minimus" <t24680@[EMAIL PROTECTED]
>
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 a definite integral, the answer depends on the value of the
antiderivative at the limits. For example, if F(x) is an
antiderivative of f(x) then the fundamental theorem of calculus tells
you that
F(b) - F(a) = integral[x=a..b] f(x) dx
There is no x on the left, and it wouldn't have mattered if the
integration variable was t. So the integrand variable is called a
dummy variable. Now what *would* be confusing is to also have one of
the a and b limits be x. Then you would be using the same symbol for
two different things. That's a no-no and isn't usually done.
--Lynn
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