F:ℝ --> ℚ x ℚ x ℚ

In order to be injective every element in my codomain is the image of at most one value of the domain.

It is NOT injective if I find an element in my codomain that is the image of more than one element of the domain.

I think the easiest thing would be to disprove it (Finding a fitting value) but I have a problem of grasping this abstract concept of mapping ℝ on a triple cartesian product.