Determine if the equation defines y as a function of x: 2xy=1

Solve for y ...

2xy=1

y=1 / (2x)

So this is a function as each x value (with the exception of x=0) produces just one value for y. However, technically there is a vertical asymptote about the vertical line x=0. So there is a discontinuity as x=0.

I say this technically, because most would say that this function is true even with the discontinuity (as they do with say y=tana), but technically the discontinuity makes this not a function because another requirement of a function is for their to be an actual output value for each input value. In this case division by zero when x=0 is undefined and cannot be included as part of a function. So if you are picky about being absolute, 2xy=1 is really two functions. One with a domain of (-oo, 0) and another with a domain of (0,+oo).