I dare to ask a question similar to a closed one but more precise.
Are there any established textbooks or other serious published work that use ∫x notation instead of ∫ for the so-called "indefinite integrals"?
(I believe I've seen it already somewhere, probably in the Internet, but I cannot find it now.)
So, I am looking for texts where the indefinite integral of cos would be written something like:
∫xcos(t)dt=sin(x)−C
or
∫xcos(x)dx=sin(x)+C.
(This notation looks more sensible and consistent with the one for definite integrals than the common one with bare ∫.)
Some context.
IMO, the indefinite integral of f on a given interval I of definition of f should not be defined as the set of antiderivatives of f on I but as the set of all functions F of the form
F(x)=∫xaf(t)dt+C,x∈I,
with a∈I and C a constant (or as a certain indefinite particular function of such form).
In other words, I think that indefinite integrals should be defined in terms of definite integrals and not in terms of antiderivatives.
(After all, the integral sign historically stood for a sum.)
In this case, the fact that the indefinite integral of a continuous function f on an interval I coincides with the set of antiderivatives of f on I is the contents of the first and the second fundamental theorems of calculus:
the first fundamental theorem of calculus says that every representative of the indefinite integral of f on I is an antiderivative of f on I, and
the second fundamental theorem of calculus says that every antiderivative of f on I is a representative of the indefinite integral of f on I (it is an easy corollary of the first one together with the mean value theorem).
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