The other part of the Fundamental Theorem (sometimes called the
first Fundamental Theorem) relates indefinite integrals
to anti-derivatives:
(First) Fundamental Theorem of Calculus:
If f is a continuous function, then
ddx∫xaf(s)ds=f(x).
That is, the indefinite integral is an anti-derivative. The
derivative of the (indefinite) integral is the original
function.
Warning: The notation ∫f(x)dx, without any upper and lower limits on the
integral sign, is used in two different ways. Sometimes it is used to mean
the indefinite integral ∫xaf(s)ds, and
sometimes it is used to mean "an anti-derivative of f(x)". Since
∫xaf(s)dsis an anti-derivative, this is consistent.