When I compute the following (with Mathematica 11.2):
Solve[(1 + r)^81 == 1.45, r]
I get a long list of solutions, all negative reals and complex numbers, apart from the one positive real answer I was expecting.
The solution list begins...
{{r -> -4.46763}, {r -> -4.45283}, {r -> -4.30803}, {r -> -4.11268}, {r -> -3.94294}....etc.
These values of r do not even remotely solve the equation, as far as I can see. Apart from anything else, they make the LHS negative, so it cannot be equal to the RHS, which is positive.
What is the meaning of these solutions? Is this just a bug in Mathematica? Or is there some sense in which they are solutions?