Question

Which of the following describes a one-to-one function?

Answer 1

check the picture below.

bearing in mind that a one-to-one function must pass the horizontal line test as well as the vertical line test.

now, |x| is the graph of a letter V more or less, and that'd fail the horizontal line test.

the first piecewise function, has say 4 : x < 0, namely for all values before 0, "y" is a steady constant of 4, that will be a horizontal line and will definitely fail the vertical line test.

[[x]] is pretty much the "floor function", and you can do a quick google search on it, or do it in your calculator, it should have a floor function, but that one will definitely fail the vertical line test as well.