And yet it's a problem anybody who makes any kind of library that should work with > 1 types, faces...
Not just math and scientific libraries. Even a simple reusable data structure. And fact it's so commonly needed for this, that Go's slices and maps would have been useless unless Go's designers have not cheated and used genericity for themselves...
And let's not get into reusable abstractions for behavior -- like a library that encapsulates the 5-10 more common uses for channels and goroutines (span N goroutines and wait for all to collect the results, span N and use first result, and so on).
A real problem is, “I need to draw this triangle”, and using math.Cos w/ float64s works just fine.