[MForster]

It also equals x with appropriate assumptions (x > 0).

[notarget137]

Well, then sin(x) = x if x is infinitely small

[kccqzy]

> Assuming[x == 0, Simplify[Sin[x] == x]]

Mathematica returns True. And any middle schooler will also tell you it's true.

The only reasonable interpretation of "infinitely small" is that it's zero.

[exe34]

so there's an unconditionally correct answer (it's also equal to abs(x) for x>0), and then there is an answer that is only correct for half the domain, which requires an additional assumption.

[crubier]

sqrt(square(i)) != abs(i)

So no, it’s not unconditionally correct either.