In WA, entering 'ax/x = a' will return 'True.'
If 'a' is replaced with a constant, it changes its rule. '7x/x = 7' will say that it's true as long as x ? 0.
Why is it that 'ax/x = a' is true until 'a' is replaced with a constant?
Mathematica was originally designed so that expressions such as a x/x are simplified to just a before any other mechanism or check could intervene. This is probably efficient for calculations, but it exposes the system to criticism. I suppose that Wolfram Alpha has new code that catches the problem, but only when the coefficient is numerical.
a x/x
a
Interestingly, in Mathematica (version 11.3) itself:
(7 x)/x == 7 (* True *) (a x)/x == a (* True *) Reduce[(7 x)/x == 7, x] (* True *) Reduce[(a x)/x == a, x] (* True *)
(Simplify applied to each equation also yields True as output.)
Simplify
True